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A&A 534, A55 (2011) Astronomy DOI: 10.1051/0004-6361/201015270 & c ESO 2011 Astrophysics

The deep XMM-Newton Survey of M 31,

H. Stiele1,W.Pietsch1, F. Haberl1, D. Hatzidimitriou2,3 R. Barnard4,5, B. F. Williams6,A.K.H.Kong7,andU.Kolb4

1 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany e-mail: [email protected] 2 Department of Astrophysics, Astronomy and Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece 3 IESL, Foundation for Research and Technology, 71110 Heraklion, Greece 4 Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK 5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 6 Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195, USA 7 Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan

Received 24 June 2010 / Accepted 11 July 2011

ABSTRACT

Aims. The largest Local Group spiral galaxy, M 31, has been completely imaged for the first time, obtaining a luminosity lower limit ∼1035 erg s−1 in the 0.2–4.5 keV band. Our XMM-Newton EPIC survey combines archival observations along the major axis, from June 2000 to July 2004, with observations taken between June 2006 and February 2008 that cover the remainder of the D25 ellipse. The main goal of the paper is to study the X-ray source population of M 31. Methods. An X-ray catalogue of 1897 sources was created, with 914 detected for the first time. Source classification and identification were based on X-ray hardness ratios, spatial extent of the sources, and cross correlation with catalogues in the X-ray, optical, infrared, and radio wavelengths. We also analysed the long-term variability of the X-ray sources and this variability allows us to distinguish between X-ray binaries and active galactic nuclei (AGN). Furthermore, supernova remnant classifications of previous studies that did not use long-term variability as a classification criterion could be validated. Including previous Chandra and ROSAT observations in the long-term variability study allowed us to detect additional transient or at least highly variable sources, which are good candidate X-ray binaries. Results. Fourteen of the 30 supersoft source (SSS) candidates represent supersoft emission of optical novae. Many of the 25 supernova remnants (SNRs) and 31 SNR candidates lie within the 10 kpc dust ring and other star-forming regions in M 31. This connection between SNRs and star-forming regions implies that most of the remnants originate in type II supernovae. The brightest sources in X-rays in M 31 belong to the class of X-ray binaries (XRBs). Ten low-mass XRBs (LMXBs) and 26 LMXB candidates were identified based on their temporal variability. In addition, 36 LMXBs and 17 LMXB candidates were identified owing to correlations with globular clusters and globular cluster candidates. From optical and X-ray colour-colour diagrams, possible high-mass XRB (HMXB) candidates were selected. Two of these candidates have an X-ray spectrum as is expected for an HMXB containing a neutron star primary. Conclusions. While our survey has greatly improved our understanding of the X-ray source populations in M 31, at this point 65% of the sources can still only be classified as “hard” sources; i.e. it is not possible to decide whether these sources are X-ray binaries or Crab-like supernova remnants in M 31 or X-ray sources in the background. Deeper observations in X-ray and at other wavelengths would help classify these sources. Key words. galaxies: individual: M 31 – X-rays: galaxies

1. Introduction After early detections of M 31 with X-ray detectors mounted on rockets (e.g. Bowyer et al. 1974)andtheUhuru satellite Our nearest neighbouring large spiral galaxy, the Andromeda (Giacconi et al. 1974), the imaging X-ray optics ﬂown on the galaxy, also known as M 31 or NGC 224, is an ideal tar- Einstein X-ray observatory permitted resolution of individual X- get for an X-ray source population study of a galaxy similar ray sources in M 31 for the ﬁrst time. In the entire set of Einstein to the Milky Way. Its proximity (distance 780 kpc, Holland imaging observations of M 31, Trinchieri & Fabbiano (1991, 1998; Stanek & Garnavich 1998) and the moderate Galactic hereafter TF91) found 108 individual X-ray sources brighter = × 20 −2 − foreground absorption (NH 7 10 cm , Stark et al. 1992)al- than ∼6.4 × 1036 erg s 1, of which 16 sources showed variabil- low detailed study of source populations and individual sources. ity (van Speybroeck et al. 1979; Collura et al. 1990).

In July 1990, the bulge region of M 31 was observed with Based on observations obtained with XMM-Newton,anESAsci- ∼ ence mission with instruments and contributions directly funded by the ROSAT High Resolution Imager (HRI) for 48 ks. Primini ESA Member States and NASA. et al. (1993, hereafter PFJ93) reported 86 sources brighter than ∼1.8 × 1036 erg s−1 in this observation. Of the ROSAT HRI sour- Tables 5 and 8 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via ces located within 7.5 of the nucleus, 18 sources were found http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/534/A55 to vary when compared to previous Einstein observations and Article published by EDP Sciences A55, page 1 of 51 A&A 534, A55 (2011) about three of the sources may be “transients”. Two deep PSPC sources they detected in five XMM-Newton observations located (Position Sensitive Proportional Counter) surveys of M 31 were along the major axis of M 31. They obtained background sub- performed with ROSAT, the first in July 1991 (Supper et al. tracted spectra and lightcurves for each of the 335 X-ray sources. 1997, hereafter SHP97) and the second in July/August 1992 Sources with more than 50 source counts were individually spec- (Supper et al. 2001, hereafter SHL2001). In total 560 X-ray trally fitted. In addition, they selected 18 HMXB candidates, sources were detected in the field of M 31; of these, 491 sources based on a power law photon index of 0.8 ≤ Γ ≤ 1.2. were not detected in previous Einstein observations. In addi- Pietsch et al. (2005b, hereafter PFH2005) prepared a cata- tion, a comparison with the results of the Einstein survey re- logue of M 31 point-like X-ray sources analysing all observa- vealed long term variability in 18 sources, including seven pos- tions available at that time in the XMM-Newton archive which sible transients. Comparing the two ROSAT surveys, 34 long overlap at least in part with the optical D25 extent of the galaxy. term variable sources and eight transient candidates were de- In total, they detected 856 sources. The central part of the galaxy tected. The derived luminosities of the detected M 31 sources was covered four times with a separation of the observations ranged from 5 × 1035 erg s−1 to 5 × 1038 erg s−1. Another impor- of about half a year starting in June 2000. PFH2005 only gave tant result obtained with ROSAT was the establishment of su- source properties derived from an analysis of the combined ob- persoft sources (SSSs) as a new class of M 31 X-ray sources (cf. servations of the central region. Source identification and clas- Kahabka 1999) and the identification of the first SSS with an sification were based on hardness ratios, and correlations with optical nova in M 31 (Nedialkov et al. 2002). sources in other wavelength regimes. In follow-up work, (i) Garcia et al. (2000) report on first observations of the nuclear Pietsch & Haberl (2005) searched for X-ray burst sources in region of M 31 with Chandra. They found that the nuclear source globular cluster (GlC) sources and candidates and identified two has an unusual X-ray spectrum compared to the other point X-ray bursters and a few more candidates; while (ii) Pietsch et al. sources in M 31. Kong et al. (2002b) report on eight Chandra (2005a, hereafter PFF2005) searched for correlations with op- ACIS-I observations taken between 1999 and 2001, which cover tical novae. They identified seven SSSs and one symbiotic star the central ∼17 ×17 region of M 31. They detected 204 sources, from the catalogue of PFH2005 with optical novae, and iden- of which ∼50% are variable on timescales of months and tified anadditional XMM-Newton source with an optical nova. 13 sources were classified as transients. Kaaret (2002) detected This work was continued and extended on archival Chandra 35 38 −1 142 point sources (LX = 2 × 10 to 2 × 10 erg s in the HRC-I and ACIS-I observations by Pietsch et al. (2007, here- 0.1–10 keV band) in a 47 ks Chandra/HRC observation of the after PHS2007). central region of M 31. A comparison with a ROSAT obser- Stiele et al. (2008, hereafter SPH2008) presented a time vari- vation taken 11 yr earlier, showed that 46 ± 26% of the sources ability analysis of all of the M 31 central sources. They de- 36 −1 with LX > 5 × 10 erg s are variable. Three different M 31 tected 39 sources not reported at all in PFH2005. 21 sources disc fields, consisting of different stellar population mixtures, were detected in the July 2004 monitoring observations of the were observed by Chandra. Di Stefano et al. (2002) investigated low mass X-ray binary RX J0042.6+4115 (PI Barnard), which bright X-ray binaries (XRBs) in these fields, while Di Stefano became available in the meantime. Six sources, which were clas- et al. (2004) examined the populations of supersoft sources sified as “hard” sources by PFH2005, show distinct time vari- (SSSs) and quasisoft sources (QSSs), including observations of ability and hence are classified as XRB candidates in SPH2008. the central field. Using Chandra HRC observations, Williams The SNR classifications of three other sources from PFH2005 et al. (2004) measured the mean fluxes and long-term time vari- had to be rejected due to the distinct time variability found by ability of 166 sources detected in these data. Voss & Gilfanov SPH2008. Henze et al. (2009a) reported on the first two SSSs (2007)usedChandra data to examine the low mass X-ray bina- ever discovered in the M 31 globular cluster system, and Henze ries (LMXBs) in the bulge of M 31. Good candidates for LMXBs et al. (2009b) discussed the very short supersoft X-ray state are the so-called transient sources. Studies of transient sources of the classical nova M31N 2007-11a. A comparative study of in M 31 are presented in numerous papers, e.g. Williams et al. supersoft sources detected with ROSAT, Chandra and XMM- (2006b), Trudolyubov et al. (2006, hereafter TPC06), Williams Newton, examining their long-term variability, was presented by et al. (2005b), Williams et al. (2006a, hereafter WGM06), and Stiele et al. (2010). Voss et al. (2008). An investigation of the log N-log S relation of sources de- Using XMM-Newton and Chandra data, Trudolyubov & tected in the 2.0–10.0 keV range will be presented in a forth- Priedhorsky (2004) detected 43 X-ray sources coincident with coming paper (Stiele et al. 2011, in prep.). In this work the con- globular cluster candidates from various optical surveys. They tribution of background objects and the spatial dependence of studied their spectral properties, time variability and log N-log S the log N-log S relations for sources of M 31 is studied. relations. In this paper we report on the large XMM-Newton survey Osborne et al. (2001)usedXMM-Newton Performance of M 31, which covers the entire D25 ellipse of M 31, for Verification observations to study the variability of X-ray the first time, down to a limiting luminosity of ∼1035 erg s−1 sources in the central region of M 31. They found 116 sources in the 0.2–4.5 keV band. In Sect. 2 information about the ob- brighter than a limiting luminosity of 6 × 1035 erg s−1 and ex- servations used is provided. The analysis of the data is pre- amined the ∼60 brightest sources for periodic and non-periodic sented in Sect. 3. Section 4 presents the combined colour im- variability. At least 15% of these sources appear to be variable age of all observations used. The source catalogue of the deep on a time scale of several months. Barnard et al. (2003)used XMM-Newton survey of M 31 is described in Sect. 5.There- XMM-Newton to study the X-ray binary RX J0042.6+4115 and sults of the temporal variability analysis are discussed in Sect. 6. suggested it as a Z-source. Orio (2006) studied the population Cross-correlations with other M 31 X-ray catalogues are dis- of SSSs and QSSs with XMM-Newton. Recently, Trudolyubov cussed in Sect. 7, while Sect. 8 discusses cross-correlations with & Priedhorsky (2008) reported the discovery of 217s pulsa- catalogues at other wavelengths. Our results related to fore- tions in the bright persistent SSS XMMU J004252.5+411540. ground stars and background sources in the field of M 31 are Shaw Greening et al. (2009, hereafter SBK2009) presented the presented in Sect. 9. Individual source classes belonging to M 31 results of a complete spectral survey of the 335 X-ray point are discussed in Sect. 10. We draw our conclusions in Sect. 11.

A55, page 2 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

3. Data analysis In this section, the basic concepts of the X-ray data reduction and source detection processes are described.

3.1. Screening for high background The first step was to exclude times of increased background, due to soft proton flares. Most of these times are located at the start or end of an orbit window. We selected good time intervals (GTIs) – intervals where the intensity was lower than a certain threshold – using 7–15 keV light curves constructed from source-free regions of each observation. The GTIs with PN and MOS data were determined from the higher statistic PN light curves. Outside the PN time coverage, GTIs were determined from the combined MOS light curves. For each observation, the limiting thresholds for the count rate were adjusted individually; this way we avoided cutting out short periods (up to a few hun- dred seconds) of marginally increased background. Short periods of low background, which were embedded within longer periods of high background, were omitted. For most observations, the PN count rate thresholds were 2–8 cts ks−1 arcmin−2. As many of the observations were affected by strong background flares, the net exposure which can be used for our analysis was strongly reduced. The GTIs of the various observations ranged over 6–56 ks, apart from observation b2 (ObsID 0202230301) which had to be rejected, because it Fig. 1. A deep optical image of M 31 (Burwitz, priv. comm.) overplotted showed high background throughout the observation. The ex- with the XMM-Newton fields of the survey. The area covered by indi- posures for all three EPIC instruments are given in Cols. 8, 10 vidual EPIC observations is approximated by circles with 14 arcmin and 12 of Table 2. The observations obtained during the summer radius. Fields observed in the “Deep XMM-Newton Survey of M 31 visibility window of M 31 were affected more strongly by back- are marked with thicker lines. For presentation purposes, the ToO ob- ground radiation than those taken during the winter window. The servation and the observations of RX J0042.6+4115 are omitted. most affected observations of the deep survey were reobserved. After screening for times of enhanced particle background, the second step was to examine the influence of solar wind charge exchange. This was done by producing soft energy (<2 keV) background light curves. These lightcurves varied only 2. Observations for ten observations, for which additional screening was necessary. The screening of enhanced background due to solar wind Figure 1 shows the layout of the individual XMM-Newton obser- charge exchange was applied to the observations only for the vations over the field of M 31. The observations of the “Deep creation of colour images, in order to avoid that these observa- XMM-Newton Survey of M 31” (PI Pietsch) mainly point at tions will appear in the mosaic image with a tinge of red. The the outer parts of M 31, while the area along the major axis screening was not used for source detection. is covered by archival XMM-Newton observations (PIs Watson, The third and last step includes the study of the back- Mason, Di Stefano). To treat all data in the same way, we re- ground due to detector noise. The processing chains take into analysed all archival XMM-Newton observations of M 31, which account all known bad or hot pixels and columns and flag the were used in Pietsch et al. (2005b). In addition we included affected pixels in the event lists. We selected data with (FLAG an XMM-Newton target of opportunity (ToO) observation of & 0xfa0000)= 0, excluded rows and columns near edges, and source CXOM31 J004059.2+411551 and the four observations searched by eye for additional warm or hot pixels and columns of source RX J0042.6+4115 (PI Barnard). in each observation. To avoid background variability over the All observations of the “Deep XMM-Newton Survey of PN images, we omitted the energy range from 7.2–9.2 keV M 31” and the ToO observation were taken between June 2006 where strong fluorescence lines cause higher background in the and February 2008. All other observations were available via the outer detector area (Freyberg et al. 2004). 1 XMM-Newton Data Archive and were taken between June 2000 An additional background component can occur during the and July 2004. EPIC PN offset map calculation. If this period is affected by high The journal of observations is given in Table 2. It includes particle background, the offset calculation will lead to a slight the M 31 field name (Col. 1), the identification number (2) and underestimate of the offset in some pixels which can then result date (3) of the observation and the pointing direction (4, 5), while in blocks of pixels (≈4 × 4) with enhanced low energy signal2. Col. 6 contains the systematic offset (see Sect. 3.4). For each These blocks will be found by the SAS detection tools and ap- EPIC camera the filter used and the exposure time after screen- pear as sources with extremely soft spectrum (so called supersoft ing for high background is given (see Sect. 3.1). sources). To reduce the number of false detections in this source

2 See also http://xmm2.esac.esa.int/docs/documents/ 1 http://xmm.esac.esa.int/xsa/ CAL-TN-0050-1-0.ps.gz

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Table 1. A selection of important X-ray surveys of M 31.

+ ∗ † Paper S #ofSrc LX Field Comments erg cm−2 s−1

Trinchieri & Fabbiano (1991, TF91) E 108 6.4 × 1036–1.3 × 1038 entire set of Einstein 16 sources showed variability (0.2–4 keV) imaging observations Primini et al. (1993, PFJ93) R (HRI) 86 ∼>1.8 × 1036 bulge region 18 sources variable; ∼3transients (0.2–4 keV) Supper et al. (1997, 2001) R (PSPC) 560 5 × 1035–5 × 1038 whole galaxy two deep surveys (SPH97, SHL2001) (0.1–2.4 keV) 491 sources not detected with Einstein 11 sources variable, 7 transients compared to Einstein 34 sources variable, 8 transients between ROSAT surveys Osborne et al. (2001) X 116 ∼>6 × 1035 centre examined the ∼60 brightest sources for variability (0.3–12 keV) Kong et al. (2002b) C (ACIS-I) 204 ∼>2 × 1035 central ∼17 × 17 observations between 1999 and 2001 (0.3–7 keV) ∼50% of the sources are variable, 13 transients Kaaret (2002) C (HRC) 142 2 × 1035–2 × 1038 centre one 47 ks observation; 46 ± 26% of the sources 36 −1 (0.1–10 keV) with LX > 5 × 10 erg s are variable Di Stefano et al. (2002)C(ACIS-I/S) 28 5 × 1035–3 × 1038 3 disc fields bright X-ray binaries (0.3–7 keV) Di Stefano et al. (2004) C (ACIS-S S3) 33 3 disc fields + centre supersoft sources and quasisoft sources Williams et al. (2004) C (HRC) 166 1.4 × 1036–5 × 1038 major axis + centre ∼>25% showed significant variability (0.1–10 keV) Trudolyubov & Priedhorsky (2004)C,X43∼1035–∼1039 major axis + centre globular cluster study (0.3–10 keV) Pietsch et al. (2005b, PFH2005) X 856 4.4 × 1034–2.8 × 1038 major axis + centre source catalogue (0.2–4.5 keV) Pietsch et al. (2005a, PFF2005) C, R, X 21 ∼1035–∼1038 centre correlations with optical novae (0.2–1 keV) Orio (2006)C,X426× 1035–∼1039 major axis + centre supersoft sources and quasisoft sources (0.2–2 keV) (0.3–10 keV) Pietsch et al. (2007, PHS2007) C, X 46 ∼1035–∼1038 centre correlations with optical novae (0.2–1 keV) Voss & Gilfanov (2007) C 263 5 × 1033–1.5 × 1038 bulge region low mass X-ray binary study (0.5–8 keV) Stiele et al. (2008, SPH2008) X 39 7 × 1034–6 × 1037 centre re-analysis of archival and new 2004 observations 300 4.4 × 1034–2.8 × 1038 time variability analysis; 149 sources with a significance (0.2–4.5 keV) for variability >3; 6 new X-ray binary candidates, 3 supernova remnant classifications were rejected Shaw Greening et al. (2009, SBK2009) X 335 ∼1034–∼1039 5 fields along background subtracted spectra and lightcurves for (0.3–10 keV) major axis each source; 18 HMXB candidates, selected from their power law photon index Stiele et al. (2010) X 40 whole galaxy supersoft sources; comparing ROSAT, Chandra and XMM-Newton catalogues Notes. (+) X-ray satellite(s) on which the study is based: E for Einstein, R for ROSAT, C for Chandra, and X for XMM-Newton (EPIC). (∗) Number of sources. (†) observed luminosity range in the indicated energy band, assuming a distance of 780 kpc to M 31. class, we decided to include the task epreject in epchain, without vignetting correction) for PN, MOS 1 and MOS 2 in which locates the pixels with a slight underestimate of the offset each of the five energy bands and masked them for the accept- and corrects this underestimate. To ensure that epreject pro- able detector area. The image bin size is 2. The same procedure duces reliable results, difference images of the event lists ob- was applied in our previous M 31 and M 33 studies (PFH2005 tained with and without epreject, were created. Only events and Pietsch et al. 2004). with energies above 200 eV were used. We checked whether To create background images, the SAS task eboxdetect was epreject removed all pixels with an enhanced low energy sig- run in local mode, in which it determines the background from nal. Only in observation ns1 the difference image still shows a the surrounding pixels of a sliding box, with box sizes of 5 × 5, block of pixels with enhanced signal. As this block is also vis- 10×10 and 20×20 pixels (10 × 10,20 × 20and 40 × 40). ible at higher energies (PHA > 30) it cannot be corrected with The detection threshold is set to likemin= 15, which is a good epreject. Additionally, we ascertained that almost all pixels compromise between cutting out most of the sources and leav- not affected during the offset map calculation have a value con- ing sufficient area to derive the appropriate background. For the sistent with zero in the difference images, with two exceptions background calculation, a two dimensional spline is fitted to a discussed in Sect. 5. rebinned and exposure corrected image (task esplinemap). The number of bins used for rebinning is controlled by the parameter 3.2. Images nsplinenodes, which is set to 16 for all but the observations of the central region, where it was set to 20 (maximum value). For For each observation, the data were split into five energy bands: PN, the background maps contain the contribution from the “out (0.2–0.5)keV, (0.5–1.0)keV, (1.0–2.0)keV, (2.0–4.5)keV, and of time (OoT)” events. (4.5–12)keV. For the PN data, we used only single-pixel = events (PATTERN 0) in the first energy band, while for the 3.3. Source detection other bands, single-pixel and double-pixel events were selected (PATTERN ≤ 4). In the MOS cameras, single-pixel to For each observation, source detection was performed simul- quadruple-pixel events (PATTERN ≤ 12) were used. We cre- taneously on five energy bands for each EPIC camera, using ated images, background images and exposure maps (with and the XMM-SAS detection tasks eboxdetect and emldetect,

A55, page 4 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 2. XMM-Newton log of the Deep Survey and archival M 31 observation overlapping with the optical D25 ellipse.

M 31 ﬁeld Obs. id. Obs. dates Pointing direction Oﬀset∗ EPIC PN EPIC MOS1 EPIC MOS2 + † + † + † RA/Dec (J2000) Filter Texp Filter Texp Filter Texp (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)

Centre 1 (c1) 0112570401 2000-06-25 0:42:36.2 41:16:58 −1.9, +0.1 medium 23.48(23.48) medium 29.64(29.64) medium 29.64(29.64) Centre 2 (c2) 0112570601 2000-12-28 0:42:49.8 41:14:37 −2.1, +0.2 medium 5.82( 5.82) medium 6.42( 6.42) medium 6.42( 6.42) Centre 3 (c3) 0109270101 2001-06-29 0:42:36.3 41:16:54 −3.2, −1.7 medium 21.71(21.71) medium 23.85(23.85) medium 23.86(23.86) N1 (n1) 0109270701 2002-01-05 0:44:08.2 41:34:56 −0.3, +0.7 medium 48.31(48.31) medium 55.68(55.68) medium 55.67(55.67) Centre 4 (c4) 0112570101 2002-01-06/07 0:42:50.4 41:14:46 −1.0, −0.8 thin 47.85(47.85) thin 52.87(52.87) thin 52.86(52.86) S1 (s1) 0112570201 2002-01-12/13 0:41:32.7 40:54:38 −2.1, −1.7 thin 46.75(46.75) thin 51.83(51.83) thin 51.84(51.84) S2 (s2) 0112570301 2002-01-24/25 0:40:06.0 40:35:24 −1.1, −0.3 thin 22.23(22.23) thin 24.23(24.23) thin 24.24(24.24) N2 (n2) 0109270301 2002-01-26/27 0:45:20.0 41:56:09 −0.3, −1.5 medium 22.73(22.73) medium 25.22(25.22) medium 25.28(25.28) N3 (n3) 0109270401 2002-06-29/30 0:46:38.0 42:16:20 −2.3, −1.7 medium 39.34(39.34) medium 43.50(43.50) medium 43.63(43.63) H4 (h4) 0151580401 2003-02-06 0:46:07.0 41:20:58 +0.3, +0.0 medium 10.14(10.14) medium 12.76(12.76) medium 12.76(12.76) RX 1 (b1)‡ 0202230201 2004-07-16 0:42:38.6 41:16:04 −1.3, −1.2 medium 16.32(16.32) medium 19.21(19.21) medium 19.21(19.21) RX 2 (b2) 0202230301 2004-07-17 0:42:38.6 41:16:04 −1.0, −0.9 medium 0.0(0.0) medium 0.0(0.0) medium 0.0(0.0) RX 3 (b3)‡ 0202230401 2004-07-18 0:42:38.6 41:16:04 −1.7, −1.5 medium 12.30(12.30) medium 17.64(17.64) medium 17.68(17.68) RX 4 (b4)‡ 0202230501 2004-07-19 0:42:38.6 41:16:04 −1.4, −1.8 medium 7.94(7.94) medium 10.12(10.12) medium 10.13(10.13) S3 (s3) 0402560101 2006-06-28 0:38:52.8 40:15:00 −3.1, −3.0 thin 4.99(4.99) medium 6.96(6.96) medium 6.97(6.97) SS1 (ss1) 0402560201 2006-06-30 0:43:28.8 40:55:12 −4.4, −3.7 thin 14.07(9.57) medium 24.56(10.65) medium 24.58(10.66) SN1 (sn1) 0402560301 2006-07-01 0:40:43.2 41:17:60 −2.7, −1.5 thin 41.23(35.42) medium 47.60(39.40) medium 47.64(39.44) SS2 (ss2) 0402560401 2006-07-08 0:42:16.8 40:37:12 −1.2, −1.3 thin 21.64(9.92) medium 25.59(11.04) medium 25.64(11.05) SN2 (sn2) 0402560501 2006-07-20 0:39:40.8 40:58:48 −0.8, −0.7 thin 48.79(21.45) medium 56.13(23.85) medium 56.17(23.86) SN3 (sn3) 0402560701 2006-07-23 0:39:02.4 40:37:48 −0.9, −2.0 thin 23.80(15.43) medium 28.02(17.16) medium 28.04(17.17) SS3 (ss3) 0402560601 2006-07-28 0:40:45.6 40:21:00 −1.8, −1.7 thin 27.77(20.22) medium 31.92(22.49) medium 31.94(22.5) S2 (s21) 0402560801 2006-12-25 0:40:06.0 40:35:24 −1.6, −0.7 thin 39.12(39.12) medium 45.19(45.19) medium 45.21(45.21) NN1 (nn1) 0402560901 2006-12-26 0:41:52.8 41:36:36 −1.5, −1.5 thin 37.9(37.9) medium 43.08(43.08) medium 43.1(43.1) NS1 (ns1) 0402561001 2006-12-30 0:44:38.4 41:12:00 −1.0, −1.3 thin 45.11(45.11) medium 50.9(50.9) medium 50.93(50.93) NN2 (nn2) 0402561101 2007-01-01 0:43:09.6 41:55:12 −0.0, −1.2 thin 41.73(41.73) medium 46.45(46.45) medium 46.47(46.47) NS2 (ns2) 0402561201 2007-01-02 0:45:43.2 41:31:48 −2.3, −1.7 thin 34.96(34.96) medium 40.55(40.55) medium 40.58(40.58) NN3 (nn3) 0402561301 2007-01-03 0:44:45.6 42:09:36 −1.4, −0.7 thin 31.04(31.04) medium 34.81(34.81) medium 34.81(34.81) NS3 (ns3) 0402561401 2007-01-04 0:46:38.4 41:53:60 −2.1, +0.3 thin 39.41(39.41) medium 45.50(45.50) medium 45.52(45.52) N2 (n21) 0402561501 2007-01-05 0:45:20.0 41:56:09 −2.6, −1.3 thin 37.18(37.18) medium 41.98(41.98) medium 42.03(42.03) SS1 (ss11) 0505760201 2007-07-22 0:43:28.8 40:55:12 −2.5, −2.6 thin 30.07(23.90) medium 34.01(26.70) medium 34.02(26.72) S3 (s31) 0505760101 2007-07-24 0:38:52.8 40:15:00 −1.8, −1.0 thin 21.86(15.74) medium 24.74(17.65) medium 24.74(17.65) CXOM31 (sn11) 0410582001 2007-07-25 0:40:59.2 41:15:51 −1.2, −0.3 thin 11.27(11.27) medium 14.01(14.01) medium 14.02(14.02) SS3 (ss31) 0505760401 2007-12-25 0:40:45.6 40:21:00 −1.0, +0.1 thin 23.56(22.82) medium 28.18(25.8) medium 28.2(25.82) SS2 (ss21) 0505760301 2007-12-28 0:42:16.8 40:37:12 +1.3, −0.1 thin 35.28(35.28) medium 40.00(40.00) medium 40.01(40.01) SN3 (sn31) 0505760501 2007-12-31 0:39:02.4 40:37:48 −1.6, −1.3 thin 24.26(24.26) medium 28.77(28.77) medium 28.78(28.78) S3 (s32) 0511380101 2008-01-02 0:38:52.8 40:15:00 −1.7, −3.3 thin 38.31(38.31) medium 44.92(44.92) medium 44.95(44.95) SS1 (ss12) 0511380201 2008-01-05 0:43:28.8 40:55:12 −0.9, −1.4 thin 8.85( 8.85) medium 11.28(11.28) medium 11.29(11.29) SN2 (sn21) 0511380301 2008-01-06 0:39:40.8 40:58:48 −0.2, −0.4 thin 24.79(24.79) medium 29.28(29.28) medium 29.29(29.29) SS1 (ss13) 0511380601 2008-02-09 0:43:28.8 40:55:12 −0.8, −1.8 thin 13.35(13.35) medium 15.07(15.07) medium 15.08(15.08)

Notes. (∗) Systematic offset in RA and Dec in arcsec determined from correlations with 2MASS, USNO-B1, LGGS and Chandra catalogues. (+) All observations in full frame imaging mode. (†) Exposure time in units of ks after screening for high background used for detection, for colour image in brackets. (‡) Combination of the three observations is called b (see text), RX denotes RX J0042.6+4115. () CXOM31 denotes CXOM31 J004059.2+411551. as such fitting provides the most statistically robust measure- simultaneously in all energy bands for all three cameras by sum- ments of the source positions by including all of the data. This ming the likelihood contribution of each band and each camera. method was also used to generate the 2XMM catalog (cf. Watson Sources exceeding the detection likelihood threshold in the full et al. 2009). In the following we describe the detection procedure band (combination of the 15 bands) are regarded as detections; used. the catalogue is thus full band selected. The source detection procedure consists of two consecutive detection steps. An initial source list is created with the task The detection threshold used is seven, as in PFH2005. Some eboxdetect (cf. Sect. 3.2). To select source candidates down other parameters differ from the values used in PFH2005, as in to a low statistical significance level, a low likelihood threshold this work a parameter setting optimised for the detection of ex- of four was used at this stage. The background was estimated tended sources was used (Lamer; priv. comm.). The parameters from the previously created background images (see Sect. 3.2). in question are the event cut-out (ecut = 30.0) and the source This list is the starting point for the XMM-SAS task selection radius (scut = 0.9) for multi-source fitting, the maxi- emldetect (v. 4.60.1). The emldetect task performs a mum number of sources into which one input source can be split Maximum Likelihood fit of the distribution of source counts (nmulsou = 2), and the maximum number of sources that can be (based on Cash C-statistics approach; Cash 1979), using a point fitted simultaneously (nmaxfit= 2). Multi-PSF fitting was per- spread function model obtained from ray tracing calculations. formed in a two stage process for objects with a detection likeli- If P is the probability that a Poissonian fluctuation in the back- hood greater than ten. All of the sources were also fitted with a β ground is detected as a spurious source, the likelihood of the convolution of a -model cluster brightness profile (Cavaliere & detection is then defined as L = − ln (P)3. The fit is performed Fusco-Femiano 1976) with the XMM-Newton point spread function, in order to detect any possible extension in the detected sig- 3 This is a simplified description as emldetect transforms the derived nal. Sources which have a core radius significantly greater than likelihoods to equivalent likelihoods, corresponding to the case of two the PSF are flagged as extended. The free parameters of the fit free parameters. This allows comparison between detection runs with were the source location, the source extent and the source counts different numbers of free parameters. in each energy band of each telescope.

A55, page 5 of 51 A&A 534, A55 (2011)

Table 3. Count rate to energy conversion factors. Sources are entered in the XMM LP-total catalogue from the observation in which the highest source detection likelihood Detector Filter B1 B2 B3 B4 B5 is obtained (either combined or single observations). For variable sources this means that the source properties given in the (1011 cts cm2 erg−1) XMM LP-total catalogue (see Sect. 5 and Table 5) are those ob- EPIC PN thin 11.33 8.44 5.97 1.94 0.58 served during their brightest state. medium 10.05 8.19 5.79 1.94 0.58 We rejected spurious detections in the vicinity of bright EPIC MOS 1 thin 2.25 1.94 2.06 0.76 0.14 sources. In regions with a highly structured background, the SAS medium 2.07 1.90 2.07 0.75 0.15 detection task emldetect registered some extended sources. We EPIC MOS 2 thin 2.29 1.98 2.09 0.78 0.15 . . . . . also rejected these “sources” as spurious detections. In an addi- medium 2 06 1 90 2 04 0 75 0 15 tional step we checked whether an object had visible contours in EPIC MOS 1 thin 2.59 2.04 2.12 0.76 0.15 OLD medium 2.33 1.98 2.09 0.76 0.15 at least one image out of the five energy bands. The point-like or EPIC MOS 2 thin 2.58 2.04 2.13 0.76 0.15 extended nature, which was determined with emldetect,was OLD medium 2.38 1.99 2.09 0.75 0.16 taken into account. In this way, “sources” that are fluctuations in the background, but which were not fully modelled in the back- Notes. The ECFs used for observations obtained before revolution 534 ground images, were detected. In addition, objects located on are marked with “OLD”. hot pixels, or bright pixels at the rim or in the corners of the individual CCD chips (which were missed during the background screening) were recognised and excluded from the source cata- To derive the X-ray flux of a source from its measured count logue, especially if they were detected with a likelihood greater rate, one uses the so-called energy conversion factors (ECF): than six in only one detector. Rate To allow for a statistical analysis, the source catalogue only Flux = (1) contains sources detected by the SAS tasks eboxdetect and ECF emldetect as described above, i.e. the few sources that were these factors were calculated using the detector response, and not detected by the analysis program, despite being visible on depended on the used filter, the energy band in question, and the the X-ray images, have not been added by hand as in previous spectrum of the source. As we wanted to apply the conversion studies (SPH2008; PFH2005). factors to all sources found in the survey, we assumed a power To classify the source spectra, we computed four hardness law model with photon index Γ=1.7 and the Galactic fore- ratios. The hardness ratios and errors are defined as: − = × 20 2 2 2 ground absorption of NH 7 10 cm (Stark et al. 1992, Bi+1 − Bi (Bi+1EBi) + (BiEBi+1) see also PFH2005) to be the universal source spectrum for the HRi = and EHRi = 2 , (2) B + + B (B + + B )2 ECF calculation. i 1 i i 1 i The ECFs (see Table 3) were derived with XSPEC4 (v 11.3.2) for i = 1to4,whereBi and EBi denote count rates and corre- using response matrices (V.7.1)available from the XMM-Newton sponding errors in energy band i. calibration homepage5. As all necessary corrections of the source parameters (e.g. vignetting corrections) were included in 3.4. Astrometrical corrections the image creation and source detection procedure6,theon axis To obtain astrometrically-corrected positions for the sources of ECF values were derived (cf. Watson et al. 2009). The fluxes the five central fields we used the SAS-task eposcorr with determined with the ECFs given in Table 3 are absorbed (i.e. ob- Chandra source lists (Kong et al. 2002b; Kaaret 2002; Williams served) fluxes and hence correspond to the observed count rates, et al. 2004). For the other fields we selected sources from the which are derived in the emldetect task. USNO-B1 (Monet et al. 2003), 2MASS (Skrutskie et al. 2006) During the mission lifetime, the MOS energy distribution and Local Group Galaxy Survey (LGGS; Massey et al. 2006) behaviour has changed. Near the nominal boresight positions, catalogues7. where most of the detected photons hit the detectors, there has been a decrease in the low energy response of the MOS cameras 3.4.1. Astrometry of optical/infrared catalogues (Read et al. 2006). To take this effect into account, different re- In a first step, we examined the agreement between the positions sponse matrices for observations obtained before and after the given by the various optical catalogues8. A close examination year 2005 were used (see Table 3). of the shifts obtained, showed significant differences between For most sources, band 5 just adds noise to the total count the positions given in the individual catalogues. In summary, be- rate. If converted to flux, this noise often dominates the total tween the USNO-B1 and LGGS catalogues we found an offset flux due to the small ECF. To avoid this problem we calculated of: −0. 197 in RA and 0. 067 in Dec9; and between the USNO- count rates and fluxes for detected sources in the “XID” (0.2– B1 and 2MASS catalogues we found an offset of: −0. 108 in 4.5) keV band (bands 1 to 4 combined). While for most sources RA and 0. 204 in Dec. We chose the USNO-B1 catalogue as a this is a good solution, for extremely hard or soft sources there reference, since it covers the entire field observed in the Deep may still be bands just adding noise. This, then, may lead to XMM-Newton survey, and in addition it provides values for the rate and flux errors that seem to falsely indicate a lower source proper motion of the optical sources. significance. A similar effect occurs in the combined rates and fluxes, if a source is detected primarily by one instrument (e.g. 7 For the remainder of the subsection we will call all three catalogues soft sources in PN). “optical catalogues” for easier readability, although the 2MASS catalogue is an infrared catalogue. 4 http://heasarc.gsfc.gov/docs/xanadu/xspec 8 From the LGGS catalogue only sources brighter than 21 mag were 5 http://xmm2.esac.esa.int/external/xmm_sw_cal/calib/ used in order to be comparable to the brightness limit of the USNO- epic_files.shtml B1 catalogue. 6 Especially in the emldetect task. 9 The offset in declination is negligible.

A55, page 6 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Since the optical catalogues, as well as the Deep XMM- merged data were used together with the data of observation c4 Newton catalogue, are composed of individual observations of to search for sources simultaneously; in this way it was possible sub-fields of M 31, we searched for systematic drifts in the posi- to take into account the different ECFs for the different filters. tional zero points from region to region. However no systematic One field was observed twice with slightly different pointing di- offsets were found. rection in observations sn1 and sn11; simultaneous source de- Finally, we applied the corrections found to the sources in tection was used for these observations as well. the LGGS and 2MASS catalogues, to bring all catalogues to the USNO-B1 reference frame. The offsets found between the USNO-B1 and 2MASS cata- 3.6. Variability calculation logues can be explained by the independent determination of the To examine the time variability of each source listed in the to- astrometric solutions for these catalogues. Given that the posi- tal source catalogue, we determined the XID flux at the source tions provided in the LGGS catalogue are corrected with respect position in each observation or at least an upper limit for the to the USNO-B1 catalogue (see Massey et al. 2006), the offset XID flux. We used the task emldetect with fixed source po- found in right ascension was totally unexpected and cannot be sitions when calculating the total flux. To get fluxes and upper explained. limits for all sources in the input list we set the detection likelihood threshold to nought. 3.4.2. Corrections of the X-ray observations A starting list was created from the full source catalogue, which only contains the identification number and position of From the positionally corrected catalogues, we selected sources each source located in the field examined. To give correct re- which either correlate with globular clusters from the Revised sults, the task emldetect has to process the sources from the Bologna Catalogue (V.3.4, January 2008; Galleti et al. 2004, brightest one to the faintest one. We, therefore, had to first or- 2005, 2006, 2007) or with foreground stars, characterised by der the sources in each observation by the detection likelihood. their optical to X-ray flux ratio (Maccacaro et al. 1988)andtheir For sources not visible in the observation in question we set the hardness ratio (see source selection criteria given in Table 6 and detection likelihood to nought. This list was used as input for Stiele et al. 2008). For sources selected from the USNO-B1 cat- afirstemldetect run. In this way we achieved an output list in alogue, we used the proper motion corrected positions. We then which a detection likelihood was allocated to every source. For a used the SAS-task eposcorr to derive the offset of the X-ray final examination of the sources in order of detection likelihood, aspect solution. Four observations did not have enough optical a second emldetect run was necessary. counterparts to apply this method. The lack of counterparts is We only accepted XID fluxes for detections ≥3σ;otherwise due to the very short exposure times resulting after the screen- we used a 3σ upper limit. To compare the XID fluxes between ing for high background (obs. s3, ss12, ss13) and the location of the different observations, we calculated the significance of the the observation (obs. sn11). In these cases, we used bright per- difference sistent X-ray sources, which we correlated with another obser- F − F vation of the same field. We checked for any residual systematic S = max min (3) uncertainty in the source positions and found it to be well char- σ2 + σ2 acterised by a conservative 1σ value of 0 . 5. This uncertainty is max min due to positional errors of the optical sources as well as inaccu- = / racy in the process of the determination of the offset between op- and the ratio of the XID fluxes V Fmax Fmin,whereFmax tical and X-ray sources, and is called systematic positional error. and Fmin are the maximum and minimum (or upper limit) source σ σ The appropriate offset, given in Col. 6 of Table 2, was applied to XID flux, and max and min are the errors of the maximum and the event file of each pointing, and images and exposure maps minimum flux, respectively. This calculation was not performed were then reproduced with the corrected astrometry. whenever Fmax was an upper limit. Finally, the highest XID flux Fields that were observed at least twice are treated in a spe- of each source was derived, excluding upper limits. cial way, which is described in the following section. 3.7. Spectral analysis 3.5. Multiple observations of selected fields To extract the X-ray spectrum of individual sources, we se- The fields that were observed more than once were the central lected an extraction region and a corresponding background re- field, the fields pointing on RX J0042.6+411510,twofieldslo- gion which was at least as large as the source region, was located on the major axis of M 31 (S2, N2) and all fields of the cated on the same CCD at a similar off axis angle as the source, “Large Survey” located in the southern part of the galaxy (SS1, and did not contain any point sources or extended emission. For SS2, SS3, S3, SN3, SN2, SN1). To reach higher detection sensi- EPIC PN, we only accepted single-pixel events for the spec- tivity we merged the images, background images and exposure tra of supersoft sources, while for all other spectra single and maps of observations which have the same pointing direction double-pixel events were used. For the EPIC-MOS detectors, and were obtained with the same filter setting. Subsequently, single-pixel through to quadruple-pixel events were always used. source detection, as described in Sect. 3.3, was repeated on the Additionally, we only kept events with FLAG = 0 for all three de- merged data. For the S2 field, there are two observations with tectors. For each extraction region, we produced the correspond- different filter settings. In this case, source detection was per- ing response matrix files and ancillary response files. formed simultaneously on all 15 bands of both observations, i.e. For each source, the spectral fit was obtained by fitting all on 30 bands simultaneously. The N2 field was treated in the same three EPIC spectra simultaneously, using the tool XSPEC.For way. For the central field images, background images and expo- the absorption, we used the TBabs model, with abundances from sure maps of observations c1, c2 and c3 were merged. These Wilms et al. (2000) and photoelectric absorption cross-sections from Bałucinska-Church´ & McCammon (1992) with a new He 10 The combination of observations b1, b3 and b4 is called b. cross-section based on Yan et al. (1998).

A55, page 7 of 51 A&A 534, A55 (2011)

Table 4. X-ray source catalogues used for cross-correlation and the used source position (including 3σ error) lies within the extent positional errors. given for the SNR. – Radio Catalogues: Gelfand et al. (2005, σccat is given for each ‡ † ‡ † σ X-ray catalogue σ X-ray catalogue σ individual source), Gelfand et al. (2004, ccat is given for ccat ccat σ = ∗ . each individual source), Kimball & Ivezic´ (2008, ccat 3 ), PFH2005 DKG2004 0 3 σ SPH2008 ∗ WNG2006 0 . 3 Braun (1990, ccat is given for each individual source), NVSS / 12 σ SHP97 ∗ VG2007 0 . 4 (NRAO VLA Sky. Survey ; Condon et al. 1998, ccat is given SHL2001 ∗ OBT2001 3 for each individual source). PFJ93 ∗ O2006 1 –HII Regions, H α Catalogue: Walterbos & Braun (1992, σccat TF91 ∗ SBK2009 3+ is given for each individual source), Massey et al. (2007, . . Ka2002 0 3 D2002 0 5 σccat = 0. 2). KGP2002 ∗ TP2004 1 σ + – Optical Catalogues: USNO-B1 (Monet et al. 2003, ccat is WGK2004 1 ONB2010 1 given for each individual source), Local Group Survey (LSG; σ = . (†) Massey et al. 2006, ccat 0 2). Notes. * Indicates that the catalogue provides σccat values for each + – Infrared catalogues: 2MASS (Skrutskie et al. 2006, σ is source individually; ( ) value taken from indicated paper. ccat given for each individual source), Mould et al. (2008, σccat = References. (‡) TF91: Trinchieri & Fabbiano (1991), PFJ93: Primini 0. 8, for Table 2: σccat = 0. 5). et al. (1993), SHP97: Supper et al. (1997), SHL2001: Supper et al. 13 (2001), OBT2001: Osborne et al. (2001), D2002: Di Stefano et al. – Data bases: The SIMBAD catalogue (Centre de Données as- tronomiques de Strasbourg; hereafter SIMBAD), the NASA (2002), KGP2002: Kong et al. (2002b), Ka2002: Kaaret (2002), 14 WGK2004: Williams et al. (2004), DKG2004: Di Stefano et al. (2004), Extragalactic Database (hereafter NED). TP2004: Trudolyubov & Priedhorsky (2004), PFH2005: Pietsch et al. (2005b), O2006: Orio (2006), WNG2006: Williams et al. (2006b), VG2007: Voss & Gilfanov (2007), SPH2008: Stiele et al. (2008), 4. Colour image SBK2009: Shaw Greening et al. (2009), ONB2010: Orio et al. (2010). Figure 2 shows the combined, exposure corrected EPIC PN, MOS 1 and MOS 2 RGB (red-green-blue) mosaic image of the Deep Survey and archival data. The colours represent the X-ray 3.8. Cross correlations energies as follows: red: 0.2–1.0keV, green: 1.0–2.0keV and Sources were regarded as correlating if their positions over- blue: 2.0–12 keV. The optical extent of M 31 is indicated by the lapped within their 3σ (99.73%) positional errors, defined as D25 ellipse and the boundary of the observed field is given by (Watson et al. 2009): the green contour. The image is smoothed with a 2D-Gaussian of 20 FWHM. In some observations, individual noisy MOS 1 Δpos ≤ 3.44 × σ2 + σ2 + 3 × σ (4) and MOS 2 CCDs are omitted. The images have not been cor- stat syst ccat rected for the background of the detector or for vignetting. The colour of the sources reflects their class. Supersoft where σ is the statistical and σ the systematic error of the stat syst sources appear in red. Thermal SNRs and foreground stars are X-ray sources detected in the present study. The statistical error orange to yellow. “Hard” sources (background objects, mainly was derived by emldetect. The determination of the system- AGN, and X-ray binaries or Crab-like SNRs) are blue to white. atic error is described in Sect. 3.4. We use a value of 0 . 5, for all Logarithmically scaled XMM-Newton EPIC low background sources. The positional error of the sources in the catalogue used images made up of the combined images from the PN, MOS 1 for cross-correlation is given by σ . The values of σ (68% ccat ccat and MOS 2 cameras in the (0.2–4.5) keV XID band for each error) used for the different X-ray catalogues can be found in M 31 observation can be found in the Appendix. The images Table 4. Exceptions to Eq. (4) are sources that are listed in more also show X-ray contours, and the sources from the XMM LP- than one catalogue or that are resolved into multiple sources with total catalogue are marked with boxes. Chandra. The first case is restricted to catalogues with comparable spatial resolution and hence positional uncertainty. To identify the X-ray sources in the field of M 31 we 5. Source catalogue (XMM LP-total) searched for correlations with catalogues in other wavelength regimes. The XMM-Newton source catalogue was correlated The source catalogue of the Deep XMM-Newton survey of with the following catalogues and public data bases: M 31 (hereafter XMM LP-total catalogue) contains 1897 X-ray sources. Of these sources 914 are detected for the first time in – Globular Clusters: Bologna Catalogue (V.3.5, March 2008; X-rays. Galleti et al. 2004, 2005, 2006, 2007, 2009, σccat = 0. 2; The source parameters are summarised in Table 5, which RBV 3.5), Caldwell et al. (2009, σccat = 0. 2), Hodge et al. gives the source number (Col. 1), detection field from which (2009, σccat = 0. 5), Krienke & Hodge (2008, σccat = 0. 2), the source was entered into the catalogue (2); source position Krienke & Hodge (2007, σccat = 0. 2), Fan et al. (2005), (3 to 9) with 3σ (99.73%) uncertainty radius (10), likelihood of Magnier (1993, σccat = 1 ). existence (11), integrated PN, MOS 1 and MOS 2 count rate and 11 – Novae: Nova list of the M 31 Nova Monitoring Project (σccat error (12, 13) and flux and error (14, 15) in the (0.2–4.5) keV is given for each individual source), PHS2007, Pietsch (2010). XID band, and hardness ratios and errors (16–23). Hardness ra- – Supernova Remnants: Dodorico et al. (1980,19srcs), tios are calculated only for sources for which at least one of the Walterbos & Braun (1992, 967 srcs) and Braun & Walterbos two band count rates has a significance greater than 2σ. Errors (1993,58srcs),Magnier et al. (1995, 233 srcs); An X-ray are the properly combined statistical errors in each band and can source is considered as correlating with a SNR, if the X-ray 12 http://www.cv.nrao.edu/nvss/NVSSlist.shtml 11 http://www.mpe.mpg.de/~m31novae/opt/m31/M31_table. 13 http://simbad.u-strasbg.fr/simbad html 14 http://nedwww.ipac.caltech.edu

A55, page 8 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Fig. 2. Combined EPIC PN, MOS 1 and MOS 2 RGB image of the Deep M 31 Survey including archival data. The optical extent of M 31 is indicated by the D25 ellipse and the boundary of the observed field is given by the green contour. The central region, marked with the yellow square, is shown in higher resolution in the upper right corner. For more details see Sect. 4. extend beyond the range of allowed values of hardness ratios as In the remaining columns of Table 5, we give information defined previously (–1.0 to 1.0; Eq. (2)). The “Val” parameter extracted from the USNO-B1, 2MASS and LGGS catalogues (Col 24) indicates whether the source is within the field of view (cf. Sect. 3.8). The information from the USNO-B1 catalogue (true or false, “T” or “F”) in the PN, MOS 1 and MOS 2 detectors (name, number of objects within search area, distance, B2, R2 respectively. and I magnitude of the brightest15 object) is given in Cols. 68 to 73. The 2MASS source name, number of objects within search Table 5 also gives the exposure time (25), source existence area, and the distance can be found in Cols. 74 to 76. Similar likelihood (26), the count rate and error (27, 28) and the flux and information from the LGGS catalogue is given in Cols. 77 to 82 error (29, 30) in the (0.2–4.5)keV XID band, and hardness ratios (name, number of objects within search area, distance, V magni- and errors (31–38) for the EPIC PN. Columns 39 to 52 and 53 tude, V − R and B − V colours of the brightest16 object). To im- to 66 give the same information corresponding to Cols. 25 to 38, prove the reliability of source classifications we used the USNO- but for the EPIC MOS 1 and MOS 2 instruments. Hardness ra- B1 B2 and R2 magnitudes to calculate tios for the individual instruments were again screened as described above. From the comparison between the hardness ra- fx mB2 + mR2 log = log ( fx) + + 5.37, (5) tios derived from the integrated PN, MOS 1 and MOS 2 count fopt 2 × 2.5 rates (Cols. 16–23) and the hardness ratios from the individual and the LGGS V magnitude to calculate instruments (Cols. 31–38, 45–52 and 59–66), it is clear that the combined count rates from all instruments yielded a significantly f m log x = log ( f ) + V + 5.37, (6) greater fraction of hardness ratios above the chosen significance f x 2.5 threshold. opt following Maccacaro et al. (1988, see Cols. 83–86). Column 67 shows cross correlations with published M 31 X- ray catalogues (cf. Sect. 3.8). We discuss the results of the cross 15 In B2 magnitude. correlations in Sects. 9 and 10. 16 In B magnitude.

A55, page 9 of 51 A&A 534, A55 (2011)

The X-ray sources in the XMM LP-total catalogue are identified or classified based on properties in X-rays (HRs, variability, extent) and of the correlated objects in other wavelength regimes (Cols. 87 and 88 in Table 5). For classified sources the class name is given in angled brackets. Identification and classification criteria are summarised in Table 6, which provides, for each source class (Col. 1), the classification criteria (2), and the numbers of identified (3) and classified (4) sources. The hardness ratio criteria are based on model spectra. Details on the definition of these criteria can be found in Sect. 6 of PFH2005. As we have no clear hardness ratio criteria to discriminate between XRBs, Crab-like supernova remnants (SNRs) or AGN we intro- duced a hard class for those sources. If such a source shows strong variability (i.e. V ≥ 10) on the examined time scales it is likely to be an XRB. Compared with SPH2008 the HR2 selection criterion for SNRs was tightened (from HR2 < −0.2to HR2 + EHR2 < −0.2) to exclude questionable SNR candidates from the class of SNRs. If we applied the former criterion to the survey data, ∼35 sources would be classified as SNRs in addition to those listed in Table 6. Most of the 35 sources are located outside the D25 ellipse, and none of them correlates with an op- tically identified SNR, a radio source, or an HII region. In addition, the errors in HR2 are of the same order as the HR2 values. Fig. 3. Distribution of the source fluxes in the 0.2–4.5 keV (XID) band. It is therefore very likely that these sources do belong to other The diagrams show the number of sources at each flux bin, plotted classes, since the strip between −0.3 < HR2 < 0 is populated by versus the flux, using logarithmic scales. The inlay shows the number − − − foreground stars, XRBs, background objects, and candidates for of sources for XID fluxes lower than 5 × 10 15 erg cm 2 s 1, on linear these three classes. Outcomes of the identification and classifi- scales. The blue histogram gives the distribution of sources classified or cation processes are discussed in detail in Sects. 9 and 10. identified as either SSSs, SNRs, XRBs or GlCs. The last column (89) of Table 5 contains the XMM-Newton source name as registered to the IAU Registry. Source names consist of the acronym XMMM31 and the source position as follows: XMMM31 Jhhmmss.s+ddmmss, where the right ascen- (Barnard et al. 2003). This source has a mean absorbed XID lu- × 38 −1 sion is given in hours (hh), minutes (mm) and seconds (ss.s) minosity of 2.74 10 erg s . truncated to decimal seconds and the declination is given in de- Figure 3 shows the distribution of the XID (0.2–4.5keV) grees (dd), arc minutes (mm) and arc seconds (ss) truncated to source fluxes. Plotted are the number of sources in a certain flux arc seconds, for equinox 2000. In the following, we refer to indi- bin. We see from the inlay that the number of sources starts to − − − vidual sources by their source number (Col. 1 of Table 5), which decrease in the bin from 2.4 to 2.6 × 10 15 erg cm 2 s 1.This is marked with a “No.” at the front of the number. XID flux roughly determines the completeness limit of the survey and corresponds to an absorbed 0.2–4.5 keV limiting lumi- Of the 1897 sources, 1247 can only be classified as hard nosity of ∼2 × 1035 erg s−1. sources, while 123 sources remain without classification. Two of ff Previous X-ray studies (Williams et al. 2004, and refer- them (No. 482, No. 768) are highly a ected by optical loading; > 37 −1 both “X-ray sources” coincide spatially with very bright optical ences therein) noted a lack of bright sources (LX ∼ 10 erg s ; foreground stars (USNO-B1 R2 magnitudes of 6.76 and 6.74 re- 0.1–10 keV) in the northern half of the disc compared to the spectively). The spectrum of source No. 482 is dominated by southern half. This finding is not supported in the present study. optical loading. This becomes evident from the hardness ratios Excluding the pointings to the centre of M 31, we found in the remaining observations 13 sources in each hemisphere that which indicate an SSS. For No. 768 the hardness ratios would al- > 37 −117 low a foreground star classification. The obtained count rates and were brighter than LXabs ∼ 10 erg s . The reason our sur- fluxes of both sources are affected by the usage of epreject, vey does not support the old results is that we found several which neutralises the corrections applied for optical loading. bright sources in the outer regions of the northern half of the disc, Therefore residuals are visible in the difference images created which have not been covered in Williams et al. (2004, and references therein). In the central field of M 31, a total of 41 sources from event lists obtained with and without epreject.Aswe > 37 −1 cannot exclude the possibility that some of the detected photons brighter than LX ∼ 10 erg s (0.2–4.5keV) were found. are true X-rays – especially for source No. 768 –, we decided Figure 4 shows the spatial distribution of the bright sources. to include them in the XMM LP-total catalogue, but without a Striking features are the two patches located north and south of classification. the centre. The southern one seems to point roughly in the direction of M 32 (No. 995), while the northern one ends in the globular cluster B 116 (No. 947). However there is no associa- 5.1. Flux distribution tion to any known spatial structure of M 31, such as the spiral arms. The faintest source (No. 526) has an XID band flux of − − − 5.8 × 10 16 erg cm 2 s 1. The source with the highest XID Flux 17 − − − The luminosity is based on XID Fluxes. Using the total 0.2–12 keV (No. 966, XID band flux of 3.75 × 10 12 erg cm 2 s 1)islo- band the result does not change (23 in the northern half and 24 in the cated in the centre of M 31 and identified as a Z-source LMXB southern half).

A55, page 10 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 6. Summary of identiﬁcations and classiﬁcations.

Source class Selection criteria Identified Classified fg Star log( fx ) < −1.0andHR2−EHR2 < 0.3andHR3−EHR3 < −0.4 or not defined 40 223 fopt AGN Radio source and not classification as SNR from HR2 or optical/radio 11 49 Gal optical id with galaxy 4 19 GCl X-ray extent and/or spectrum 1 5 SSS HR1 < 0.0, HR2−EHR2 < −0.96 or HR2 not defined, HR3, HR4 not defined 30 SNR HR1 > −0.1andHR2+EHR2 < −0.2 and not a fg Star, or id with optical/radio SNR 25 31 GlC optical id 36 16 XRB optical id or X-ray variability 10 26 hard HR2−EHR2 > −0.2oronlyHR3and/or HR4 defined, and no other classification 1247

Fig. 4. XMM-Newton Deep Survey image over plotted with sources that have an absorbed 0.2–4.5 keV luminosity higher than 1037 erg s−1. Striking features are the two patches located north and south of the centre. The central region (same as in Fig. 2) is shown with higher resolu- Fig. 5. Exposure map of all ﬁelds of the XMM LP-total catalogue. For tion in the upper right corner. details see Sect. 5.2.

5.3. Hardness ratio diagrams We plot X-ray colour/colour diagrams based on the HRs (see 5.2. Exposure map Fig. 6). Sources are plotted as dots if the error in both contributing HRs is below 0.2. Classified and identified sources are plot- Figure 5 shows the exposure map used to create the colour im- ted as symbols in all cases. Symbols including a dot therefore age of all XMM-Newton Large Survey and archival observations mark the well-defined HRs of a class. (Fig. 2). The combined MOS exposure was weighted by a fac- From the HR1-HR2 diagram (upper panel in Fig. 6) we note tor of 0.4, before being added to the PN exposure. However, this that the class of SSSs is the only one that can be defined based on map does not quite represent the exposures used in source de- hardness ratios alone. In the part of the HR1-HR2 diagram that tection; overlapping regions were not combined during source is populated by SNRs, most of the foreground stars and some detection. background objects and XRBs are also found. From Fig. 5 we see that the exposure for most of the sur- Foreground star candidates can be selected from the veyed area is rather homogeneous. Exceptions are the central HR2-HR3 diagram (middle panel in Fig. 6), where most of them area, overlapping regions and observation h4. are located in the lower left corner. The HR3-HR4 diagram

A55, page 11 of 51 A&A 534, A55 (2011)

Fig. 7. Distribution of extent parameter.

(lower panel in Fig. 6) does not help to disentangle the diﬀer- ent source classes. Thus, we need additional information from correlations with sources in other wavelengths or on the source variability or extent to be able to classify the sources.

5.4. Extended sources The XMM LP-total catalogue contains 12 sources which are fitted as extended sources with a likelihood of extension higher than 15. This value was chosen so as to minimise the number of spurious detections of extended sources (Brunner; priv. comm.), as well as keeping all sources that can clearly be seen as extended sources in the X-ray images. A convolution of a β-model cluster brightness profile (Cavaliere & Fusco-Femiano 1976) with the XMM-Newton point spread function was used to determine the extent of the sources (cf. Sect. 3.3). This model describes the brightness profile of galaxy clusters, as

−3/2 (x − x )2 + (y − y )2 f (x,y) = + 0 0 , 1 2 (7) rc

where rc denotes the core radius; this is also the extent parameter given by emldetect. Table 7 gives the source number (Col. 1), likelihood of detection (2), the extent found (3) and its associated error (4) in arcsec, the likelihood of extension (5), and the classiﬁcation of the source (6, see Sect. 9.2) for each of the 12 extended sources. Additional comments taken from Table 5 are provided in the last column. The extent parameter found for the sources ranges from 6. 2 to 23. 03 (see Fig. 7). The brightest source (No. 1795), which has the highest likelihood of extension and the second largest extent, was identiﬁed from its X-ray properties as a galaxy cluster located behind M 31 (Kotov et al. 2006). The iron emission lines in the X-ray spectrum yield a cluster redshift of z = 0.29. For further discussion see Sect. 9.2.

6. Variability between XMM-Newton observations To examine the long-term time variability of each source, we Fig. 6. Hardness ratios of sources detected by XMM-Newton EPIC. determined the XID flux at the source position in each observa- Sources with HR errors smaller then 0.20 on both HR(i)andHR(i + 1) tion or at least an upper limit for the XID flux. The XID fluxes are shown as dots. Foreground stars and candidates are marked as big were used to derive the variability factor and the significance of and small stars, AGN and candidates as big and small crosses, back- variability (cf. Sect. 3.6). ground galaxies and galaxy clusters as big “X” and their candidates as The sources are taken from the XMM LP-total catalogue small “X”, SSS candidates as triangles, SNRs and candidates as big (Table 5). Table 8 contains all information necessary to exam- and small octagons, GlCs and XRBs as big squares and their candidates ine time variability. Sources are only included in the table if they as small squares. are observed at least twice. Column 1 gives the source number. Columns 2 and 3 contain the flux and the corresponding error in

A55, page 12 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 7. Extended sources in the XMM LP-total catalogue.

SRC DET_ML EXT+ EEXT+ EXT_ML XFLUX∗ XEFLUX∗ Class Comment† (1) (2) (3) (4) (5) (6) (7) (8) (9) 141 65.08 11.22 1.29 23.68 1.45 0.20 GCl GLG127(Gal), 37W 025A (IR, RadioS; NED) 199 275.16 17.33 1.05 174.73 4.31 0.29 hard 252 222.05 14.64 1.12 81.60 4.40 0.49 GCl ﬁve optical objects in error box 304 299.75 15.10 0.92 133.62 2.20 0.18 GCl B242 [CHM09]; RBC3.5: GlC 442 33.76 11.60 1.71 15.44 1.62 0.28 hard 618 271.08 6.20 0.73 42.86 3.15 0.21 hard 718 77.75 7.18 1.23 21.47 0.58 0.07 Gal B052 [CHM09], RBC3.5 1130 168.31 10.80 0.97 44.23 3.27 0.31 hard 1543 70.49 11.87 1.37 28.63 1.51 0.19 GCl [MLA93] 1076 PN (SIM,NED) 1795 11 416.36 18.79 0.29 4169.74 98.87 1.43 GCl GLG253 (Gal), [B90] 473, z = 0.3 [KTV2006] 1859 107.09 13.73 1.40 43.89 1.23 0.19 hard 1912 332.06 23.03 1.23 213.90 5.43 0.37 GCl cluster of galaxies candidate

Notes. (+) Extent and error of extent in units of 1;1 corresponds to 3.8 pc at the assumed distance of M 31. (∗) XID Flux and flux error in units of 1 × 10−14 erg cm−2 s−1. (†) Taken from Table 5. the (0.2–4.5) keV XID band. The hardness ratios and errors are given in Cols. 4 to 11. Column 12 gives the type of the source. All this information was taken from Table 5. The subsequent 140 columns provide information related to individual observations in which the position of the source was observed. Column 13 gives the name of one of these observations, which we will call observation 1. The EPIC instruments contributing to the source detection in observation 1, are indicated by three characters in the “obs1_val” parameter (Col. 14, first character for PN, second MOS 1, third MOS 2), each one being either a “T” if the source is inside the FoV, or “F” if it lies outside the FoV. Then the count rate and error (15, 16) and flux and error (17, 18) in the (0.2–4.5) keV XID band, and hardness ratios and error (19–26) of observation 1 are given. Corresponding information is given for the remaining observations which cover the position of the source: obs. 2 (Cols. 27–40), obs. 3 (41–54), obs. 4 (55–68), obs. 5 (69–82), obs. 6 (83–96), obs. 7 (97–110), obs. 8 (111–124), obs. 9 (125–138), obs. 10 (139–152). Whether the columns corresponding to obs. 3–obs. 10 are filled in or not, depends on Fig. 8. Variability factor of sources from the XMM LP-total cata- the number of observations in which the source has been cov- logue in the 0.2–4.5 keV band derived from average fluxes of the ered in the combined EPIC FoV. This number is indicated in XMM-Newton EPIC observations plotted versus maximum detected Col. 153. The maximum significance of variation and the max- flux (erg cm−2 s−1). Source classification is indicated: Foreground stars imum flux ratio (fvar_max) are given in Cols. 154 and 155. As and candidates are marked as big and small stars, AGN and candidates described in Sect. 3.6, only detections with a significance greater as big and small crosses, background galaxies and galaxy clusters as than 3σ were used, otherwise the 3σ upper limit was adopted. big “X” and their candidates as small “X”, SSS candidates as triangles, Column 156 indicates the number of observations that provide SNRs and candidates as big and small octagons, GlCs and XRBs as big only an upper limit. The maximum flux (fmax) and its error are squares and their candidates as small squares. Sources with a statistical significance for the variability below three are marked in green. given in Cols. 157 and 158. In a few cases a maximum flux value could not be derived, because each observation only yielded an upper limit. There can as AGN, background galaxies or galaxy clusters all show Fvar < be two reasons for this: the first reason is that faint sources de- 4. Most of the foreground stars show Fvar < 4. tected in merged observations may not be detected in the indi- Out of the 1407 examined sources, we found 317 sources vidual observations at the 3σ limit. The second reason is that in with a variability significance >3.0, i.e. 182 more than reported cases where the significance of detection was not much above in SPH2008. For bright sources it is much easier to detect vari- the 3σ limit, it can become smaller than the 3σ limit when the ability than for faint sources, because the difference between source position is fixed to the adopted final mean value from all the maximum observed flux and the detection limit is larger. observations. Therefore the significance of the variability declines with de- Figure 8 shows the variability factor plotted versus maxi- creasing flux. This is illustrated by the distribution of the sources mum detected XID flux. Apart from XRBs, or XRBs in GlCs, marked in green in Fig. 8. or candidates of these source classes, which were selected based Table 9 lists all sources with a variability factor greater than on their variability, there are a few SSS candidates showing pro- five. There are 69 such sources (34 in addition to SPH2008). nounced temporal variability. The sources classified or identified The sources are sorted in descending order with respect to their

A55, page 13 of 51 A&A 534, A55 (2011)

Table 9. Variable sources with ﬂux variability greater than ﬁve, ordered by variability.

Source Fvar Svar Fmax‡ Efmax‡ Class+ Comment†

523 692.64 63.33 106.61 1.68 XRB 1032 660.61 54.21 33.89 0.62 GlC 1(t, 92.2), 11, 16, 27(831.10) 57 644.03 96.796 147.76 1.52 XRB 1131 558.48 80.18 38.93 0.48 XRB 1(t, 954.2), 2(t, 2163), 19, 20(t), 22, 26, 27(624.05) 944 236.47 44.74 24.24 0.54 XRB 1(t, 370.5), 14(t, BH-XRN), 20(t), 21(v,t), 26, 27(353.67) 705 185.02 39.85 32.52 0.81 XRB 3(t), 27(178.79) 1007 161.84 42.33 44.30 1.04 XRB 1, 12, 13, 26, 27(12.96) 1195 144.47 36.95 28.51 0.76 SSS 2(t, 694), 14(v,t), 20(t), 26, 27(82.68) 1152 123.95 55.31 31.86 0.56 XRB 1(t, 96.3), 2(t, 107), 9, 11(v), 12, 13(v), 19, 21(v,t), 26, 27(131.73) 788 117.83 20.99 12.27 0.58 XRB 1(t, 20.8), 2(t, 93), 11, 14(t), 20(t), 26, 27(97.89) 1136 87.84 25.00 9.79 0.39 XRB 1(t, 46.1), 2(t, 155), 19, 20(t), 23, 26, 27(97.65) 934 84.94 28.35 21.26 0.90 SSS 949 80.16 25.55 17.75 0.68 XRB 2(t, 13), 20, 25, 26 1194 75.22 39.69 12.79 0.31 SSS 1, 2(t, 96), 9, 12, 13(v), 14(v), 19(v), 21(v), 26, 27(85.93) 1416 72.25 21.00 10.51 0.49 SSS 26, 28 1084 59.11 8.70 6.64 0.75 XRB 1(t, 79.0), 2(t, 260), 14(t), 18, 20(t), 21(v,t), 26, 27(57.41) 985 51.66 80.00 80.46 0.97 XRB 3(t), 5(t, LMXB), 9, 21(v), 27(76.27) 1017 49.85 20.73 9.64 0.45 XRB 1(t, 99.5), 2(t, 158), 21(v,t), 26, 27(38.07) 990 48.90 61.77 82.16 1.28 XRB 1(t, 468.8), 2(t, 285), 14(v,t, BH-XRT), 18(t), 21(v,t), 26, 27(201.71) 1059 48.10 23.64 9.16 0.37 XRB 1(t, 64.6), 27(39.69) 698 41.20 18.73 9.33 1.37 XRB 13, 23, 26, 27(44.67) 884 32.88 9.59 2.84 0.61 XRB 1, 27(24.95) 1153 31.06 17.96 4.22 0.22 XRB 1(t), 3(t), 6(t, LMXB), 27(30.50) 1000 26.86 20.17 5.75 0.48 1(t), 19, 21, 23, 26, 27(34.47) 1024 25.66 78.46 144.02 1.89 XRB 1, 9, 11, 12, 13, 19, 21(v), 26, 27(34.02) 1177 24.00 19.31 4.59 0.22 XRB 3(t), 27(27.06) 939 22.48 10.13 2.20 0.20 XRB 1(t, 65.2), 27(28.02) 960 21.56 9.497 5.51 0.55 fg Star 1, 12, 13, 19, 21, 23, 26, 27(21.97) 1180 16.48 17.16 7.53 0.40 XRB 1, 12, 19, 21(v), 26, 27(13.01) 378 16.21 9.39 6.83 0.98 XRB 25, 26 714 14.89 13.77 10.35 0.68 fg Star 748 14.45 13.86 3.62 0.23 SSS 25, 26, 27(14.18) 92 14.23 5.73 1.86 0.30 SSS 814 13.66 7.98 4.94 0.56 XRB 1, 21(v), 25, 26, 27(15.76) 1006 11.30 14.34 1.44 0.08 SSS 2(t, 51), 19, 23, 26, 27(10.70) 542 10.90 3.26 2.50 0.69 XRB 1016 10.46 20.66 6.37 0.26 XRB 1, 11 ,12, 19, 21, 26, 27(11.69) 1144 10.23 10.53 1.54 0.12 SSS 2(t, 38), 26, 27(10.05) 1034 10.11 28.93 9.81 0.28 XRB 1, 19, 21, 23, 27(10.24) 1099 9.95 4.50 5.12 1.01 hard 25, 26 904 9.16 8.65 8.55 0.84 hard 12, 26 872 9.13 17.16 7.31 0.38 GlC 1, 7, 19 , 21(v), 26, 27(7.48) 1422 9.06 2.99 1.87 0.55 hard 1183 7.66 11.93 8.43 0.57 hard 12, 13, 26 422 7.23 9.65 2.10 0.16 hard 13 823 7.16 28.29 20.25 1.30 GlC 1, 4, 11, 14(v), 15, 19, 21(v), 26, 27(6.45) 1250 6.94 2.80 0.89 0.27 SSS 398 6.79 2.93 1.79 0.52 hard 13, 26 1266 6.67 7.54 2.37 0.24 GlC 4, 26, 27(8.27) 975 6.58 7.98 1.76 0.35 GlC 1, 4, 13, 15, 19, 20, 21(v), 26 522 6.47 6.62 2.21 0.26 hard 805 6.22 3.66 0.96 0.21 hard 916 6.21 3.73 2.00 0.44 hard 862 6.17 5.33 1.38 0.20 GlC 1, 4, 15, 21, 26, 27(5.35) 1124 6.04 12.93 5.73 0.23 GlC 1, 19, 20, 21(v), 26 430 5.98 4.95 1.01 0.16 hard 1825 5.57 6.11 2.97 0.39 fg Star 13, 26 1494 5.55 4.06 0.95 0.18 hard 26 624 5.54 7.58 1.49 0.13 fg Star 1167 5.44 7.69 3.22 0.57 hard 1, 19, 20, 21(v), 26 1450 5.44 6.51 2.24 0.24 hard 66 5.39 3.80 2.31 0.49 hard 1655 5.34 4.72 1.50 0.24 hard 964 5.30 6.36 1.09 0.12 hard 226 5.28 3.29 0.56 0.13 hard 244 5.27 9.08 3.33 0.28 hard 13, 25, 26 1361 5.21 3.12 1.36 0.34 hard 27 933 5.19 4.99 8.73 1.30 GlC 4, 11, 12, 25, 26 1366 5.13 3.02 1.05 0.27 hard

Notes. (‡) Maximum ﬂux and error in units of 1 × 10−14 erg cm−2 s−1 or maximum luminosity and error in units of 7.3 × 1035 erg s−1; (+) class according to Table 6. References. (†) 1: Voss & Gilfanov (2007), 2: Williams et al. (2006b), 3: Trudolyubov et al. (2006), 4: Trudolyubov & Priedhorsky (2004), 5: Williams et al. (2006a), 6: Williams et al. (2005b), 7: Pietsch & Haberl (2005), 8: Kong et al. (2003), 9: Trinchieri & Fabbiano (1991), 10: Collura et al. (1990), 11: Primini et al. (1993), 12: Supper et al. (1997), 13: Supper et al. (2001), 14: Osborne et al. (2001), 15: Di Stefano et al. (2002), 16: Fan et al. (2005), 17: Pietsch et al. (2007), 18: Garcia et al. (2000), 19: Kaaret (2002), 20: Williams et al. (2004), 21: Kong et al. (2002b), 22: Williams et al. (2005a), 23: Di Stefano et al. (2004), 24: Barnard et al. (2003), 25: Shaw Greening et al. (2009), 26: Pietsch et al. (2005b), 27: Stiele et al. (2008), 28: Trudolyubov et al. (2002) ; t: transient, v: variable, sv: spectrally variable, r: recurrent, d: dipping, z: Z-source candidate; BH: black hole, XRN: X-ray nova, XRT: X-ray transient, LMXB: low mass X-ray binary, NS: neutron star; numbers indicate the variability given by the corresponding paper.

A55, page 14 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 10. Sources with maximum flux higher than 8 × 10−13 erg cm−2 s−1, a statistical significance of variability greater than ten and a flux variability lower than five, ordered by flux.

Source Fvar Svar Fmax‡ Efmax‡ Class+ Comment† 966 1.63 49.01 46.73 0.59 XRB 1(sv,z), 2, 10(v), 12(v), 13, 14, 20, 22(v), 25(LMXB), 27, 28(1.56) 877 3.13 49.13 16.06 0.20 hard 1(sv), 2, 10(v), 12(v), 13, 14, 20(v), 22(v), 27, 28(3.05) 745 2.43 26.89 12.65 0.18 AGN 13, 14 1157 1.32 11.10 9.87 0.25 GlC 1(sv), 2, 5, 10, 12, 13, 14, 20, 21, 22(v), 27, 28(1.37) 1060 2.13 30.00 9.04 0.14 XRB 1(sv), 2, 10, 12, 13, 14, 20(v, NS-LMXB), 22(v), 27 1171 4.14 18.86 9.02 0.41 GlC 1(d,sv), 2(t, 53.4), 5, 10, 12, 13, 14, 16, 20, 22, 27, 28(2.47) 1116 3.76 51.98 8.16 0.10 GlC 1(sv), 2(t, 58.6), 3(t, 33), 5, 10, 12, 13, 14, 16, 20, 21, 22(v,t), 27

Notes. (‡) Maximum XID ﬂux and error in units of 1 × 10−13 erg cm−2 s−1 or maximum absorbed 0.2–4.5 keV luminosity and error in units of 7.3 × 1036 erg s−1; (+) class according to Table 6; (†) for comment column see Table 9.

Fig. 9. Variability factor of sources from the XMM LP-total catalogue in the 0.2–4.5 keV band (derived from the average fluxes of the XMM-Newton EPIC observations) plotted versus HR1 in the left panel and HR2 in the right panel. For source classification see Fig. 8. Sources with a statistical significance of the variability below three are marked in green.

variability factors. Table 9 gives the source number (Col. 1), sources are SSS candidates, while six variable sources are clas- maxima of flux variability (2) and maxima of the significance sified as foreground stars and foreground star candidates. parameter (3). The next Cols. (4, 5) indicate the maximum ob- Table 10 lists all “bright” sources with a maximum flux served flux and its error. Column 6 contains the class of the − − − higher than 8 × 10 13 erg cm 2 s 1 and a flux variability lower source. Sources with F ≥ 10 that were not already classified var than five (the description of the columns is the same as in as SSS or foreground stars, were classified as XRB. Table 9). All seven sources listed in Table 10 (three in addi- Time variability can also be helpful to verify a SNR can- tion to SPH2008) have a significance of variability >10. Apart didate classification. If there is significant variability, the from two sources, they are XRBs (three in globular clusters) SNR classification must be rejected, and if an optical counter- or XRB candidates. The most luminous source in our sample part is detected, the source has to be re-classified as foreground is source No. 966 with an absorbed 0.2–4.5 keV luminosity of star candidate. Column 7 contains references to the individual ≈3.3 × 1038 erg s−1 at maximum. sources in the literature. In some cases the reference provides Figure 9 shows the relationship between the variability factor information on the temporal behaviour and a more precise clas- and the hardness ratios HR1 and HR2, respectively. The hard- sification (see brackets). The numbers given in connection with Voss & Gilfanov (2007)andWilliams et al. (2006b) are the vari- ness ratios are taken from Table 5. The HR1 plot shows that the sample of highly variable sources includes SSS and XRB can- ability factors obtained in these papers from Chandra data. From didates, which occupy two distinct regions in this plot (see the 69 sources of Table 9, ten show a flux variability greater than 100. With a flux variability factor >690 source No. 523 is also Haberl & Pietsch 1999, for the LMC). The SSSs marked by triangles, appear on the left hand side, while the XRBs or the most variable source in our sample. Source No. 57 has the XRB candidates have much harder spectra, and appear on the largest significance of variability, with a value of ≈97. The variability significance is below ten for just 33 sources, 15 of which right. It seems that foreground stars, SSSs and XRBs can be separated, on the HR2 diagram, although there is some overlap be- show significance values below five. Thirty-five of the variable tween foreground stars and XRBs. sources are classified as XRBs or XRB candidates, and eight of them are located in globular clusters. Nine of the variable Individual sources are discussed in the Sects. 9 and 10.

A55, page 15 of 51 A&A 534, A55 (2011)

Table 11. Sources from previous XMM-Newton studies that are not listed in the XMM LP-total catalogue.

PFH2005 856 sources 103 not detected 6 not detected, LH > 100: 327 ( SNR ,LH= 2140.0), 384 (XRB, 667.0), 332 ( SNR , 654.0), 316 ( SNR , 259.0), 312 ( SNR , 241.0), 281( hard , 160.0) 10 not detected, 20 ≤ LH < 50: 75 ( SSS ), 423 ( fg Star ), 120 ( hard ), 505 ( hard ), 220 ( SNR ), 304 ( fg Star ), 819 ( hard ), 799 ( SSS ), 413 ( SNR ), 830 ( hard ) 14 not detected, 15 ≤ LH < 20: 427( hard ), 734 ( hard ), 424 ( hard ), 518 ( SSS ), 232 ( hard ), 339 ( hard ), 446 ( SSS ), 219 ( fg Star ), 567 ( hard ), 256 ( fg Star ), 356 ( hard ), 248 ( hard ), 160 ( hard ), 399 () 21 not detected, 10 ≤ LH < 15: 375 ( hard ), 17 ( hard ), 195 ( hard ), 417 ( SNR ), 783 ( hard ), 803 ( hard ), 829 ( hard ), 135 ( hard ), 151 ( hard ), 131 ( hard ), 426 ( hard ), 593 ( fg Star ), 526 ( hard ), 250 ( hard ), 62 ( hard ), 67 ( hard ), 188 ( hard ), 186 ( AGN ), 510 ( hard ), 529 ( hard ), 754 ( hard ) 52 not detected, LH ∼< 10: 599 ( hard ), 439 ( hard ), 809 ( hard ), 14 ( SNR ), 743 ( hard ), 433 ( hard ), 5 (), 210 ( hard ), 97 ( hard ), 708 ( hard ), 476 (), 534 ( hard ), 501 (), 170 ( hard ), 146 (SNR), 769 (), 838 ( hard ), 571 ( hard ), 816 ( hard , 554 (), 627 ( hard ), 464 ( fg Star ), 811 ( hard ), 655 ( hard ), 184 ( hard ), 447 ( hard ), 380 ( hard ), 566 ( hard ), 137 ( fg Star ), 63 (), 48 (), 152 ( fg Star ), 291 ( hard ), 559 ( hard ), 102 ( hard ), 740 ( hard ), 540 ( fg Star ), 240 ( hard ), 485 (), 668 ( hard ), 44 (), 560 ( hard ), 836 ( hard ), 436 ( hard ), 484 ( fg Star ), 216 ( hard ), 362 ( hard ), 527 ( ), 179 ( hard ), 834 ( hard ), 86 ( hard ), 455 () SPH2008 39 sources 15 not detected 3 not detected, 50 ≤ LH < 100: 874 ( SNR ,LH= 85.5), 895 ( hard , 75.9), 882 ( ,56.4) 6 not detected, 10 ≤ LH < 50: 869 (), 885 ( SNR ), 863 ( hard ), 875 ( SSS ), 893 ( hard ), 866 ( hard ) 6 not detected, LH < 10: 870 ( SNR ), 891 ( hard ), 889 ( hard ), 872 ( SNR ), 867 ( hard ), 862 ( SNR ) SBK2009 335 sources 31 not detected 4( hard ), 18 ( hard ), 29 ( hard ), 32 ( hard ), 34 ( hard ), 45 ( SSS ), 67 ( hard ), 102 ( hard ), 106 ( hard ), 117 ( hard ), 149 ( hard ), 152 ( hard ), 179 ( hard ), 183 ( hard ), 184 ( hard ), 188 ( hard ), 191 ( hard ), 192 ( AGN ), 202 ( hard ), 204 ( fg star ), 217 ( hard ), 249 ( hard ), 250 ( hard ), 260 ( hard ), 274 ( hard ), 279 ( hard ), 285 ( hard ), 295 ( hard ), 306 ( hard ), 325 ( hard ), 333 ( hard )

7. Cross-correlations with other M 31 X-ray files applied. The search strategy of PFH2005 was optimised catalogues to detect sources located close to each other in crowded fields. This point especially explains the non-detection of the bright Cross-correlations were determined by applying Eq. (4)tothe PFH2005 sources [PFH2005] 281, 312, 316, 327, 332, 384 sources of the XMM LP-total catalogue and to sources reported (L > 50) in the present study, as four of them ([PFH2005] 312, in earlier X-ray catalogues. The list of X-ray catalogues used is 316, 327, 332) are located in the innermost central region of given in Table 4. M 31 where source detection is complicated by the bright diffuse X-ray emission, while [PFH2005] 281 and 384 lie in the immediate vicinity of two bright sources ([PFH2005] 280 and 7.1. Previous XMM-Newton catalogues 381 at distances of 7.7 and 5.5, respectively). The changes in the SAS versions and the GTIs, in particular, affect sources with Previous source lists based on archival XMM-Newton obser- low detection likelihoods (L < 10). vations were presented in Osborne et al. (2001), PFH2005, Orio (2006), SPH2008, and SBK2009. Of these four studies, The improvements in the SAS detection tools and calibration PFH2005 covers the largest area of M 31. Table 11 lists all files should reduce the number of spurious detections, which in- sources from previous XMM-Newton studies that are not decrease with decreasing detection likelihood. However, this does tected in the present investigation. not necessarily imply that all undetected sources with L < 10 of In the ten observations covering the major axis, and a field PFH2005 are spurious detections. The changes in the SAS ver- in the halo of M 31, PFH2005 detected 856 X-ray sources with sions, calibration files and GTIs do not only affect the source a detection likelihood threshold of seven (cf. Sect. 3.3). Of these detection tasks, but also can cause changes in the background 856 sources, only 753 sources are also present in the XMM LP- images. These changes may increase the assumed background total catalogue, i.e. 103 sources of PFH2005 were not detected. value at the position of a source, which would result in a lower This can be due to: the search strategy; the parameter settings detection likelihood. Going from mlmin = 7 to mlmin = 6,but used in the emldetect run; the determination of the extent leaving everything else unchanged, we detected an additional of a source for the XMM LP-total catalogue; the more severe nine sources of PFH2005. One of the previously undetected screening for GTIs for the XMM LP-total catalogue, which led sources ([PFH2005] 75) was classified as SSS , but correlates to shorter final exposure times; the use of the epreject task with blocks of pixels with enhanced low energy signal in the and last but not least due to the SAS versions and calibration PN offset map and was corrected by epreject. Another source

A55, page 16 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31 classified as SSS ([PFH2005] 799) is only detected in the in Table 12. Here, we only give a few general remarks. A MOS 1 camera, but not in MOS 2. From an examination by eye, non-negligible number of Chandra sources not reported in it seems that source [PFH2005] 799 is the detection of some the XMM LP-total catalogue have already been classified as noisy pixels at the rim of the MOS 1 CCD 6 and not a real X-ray transient or variable sources. Thus, it is not surprising that source. these sources were not detected in the XMM-Newton observa- SPH2008 extended the source catalogue of PFH2005 by re- tions (parts of: Voss & Gilfanov 2007; Williams et al. 2006b, analysing the data of the central region of M 31 and also DKG2004). One Chandra source (n1-66) lies outside the field of including data of monitoring observations of LMXB M31coveredbytheXMM-Newton observations. For the inner- RX J0042.6+4115. Of the 39 new sources presented in most central region of M 31, the point spread function of XMM- SPH2008, 24 are also listed in the XMM LP-total catalogue, i.e. Newton causes source confusion and therefore only Chandra ob- 15 sources of SPH2008 were not detected. Differences between servations are able to resolve the individual sources, especially if the two studies include the detection likelihood thresholds used they are faint compared to the diffuse emission or nearby bright for eboxdetect (SPH2008: likemin = 5) and emldetect sources (Kong et al. 2002b; Kaaret 2002; Williams et al. 2004, (SPH2008: mlmin = 6), the lower limit for the likelihood of 2006b; Di Stefano et al. 2004; Voss & Gilfanov 2007). This ex- extention (SPH2008: dmlextmin= 4; XMM LP-total: 15), plains why a certain number of these sources are not detected in the screening for GTIs, the use of the epreject task and the XMM-Newton observations. SAS versions and calibration files used. Concerning the GTIs, Of the 28 bright X-ray sources located in globular clus- images, background images and exposure maps SPH2008 ters (Di Stefano et al. 2002), two were not found in the followed the same procedures as in PFH2005. The arguments XMM-Newton data (see Table 12). They are also not included given above are therefore also valid here. From the 14 unde- in the source catalogue of PFH2005 and SPH2008. Hence, both tected sources, three sources were detected in SPH2008 with objects are good candidates for being transient or at least highly mlmin < 7. One source ([SPH2008] 882) was added by hand variable sources (cf. Sect. 10.4.2). Another study of the glob- to the final source list, as SPH2008 could not find any reason ular cluster population of M 31 is presented by Trudolyubov why emldetect did not automatically find it. The two extended & Priedhorsky (2004). Their work is based on XMM-Newton sources ([SPH2008] 863, 869) detected with extent likelihoods and Chandra data and contains 43 X-ray sources. Of these between 4.7 and 5.1 in SPH2008, are neither detected as sources three were not found in the present study. One of them extended nor as pointlike sources in the present study, where the ([TP2004] 1) is located well outside the field of M 31 cov- extent likelihood has to be higher than 15. ered by the Deep XMM-Newton Survey18. The second source SBK2009 re-analysed the XMM-Newton observations lo- ([TP2004] 21) correlates with r3-71, which is discussed above cated along the major axis of M 31, ignoring all observations (see Di Stefano et al. 2002 in Table 12). The transient nature of pointing to the centre of the galaxy. They used a detection likeli- the third source ([TP2004] 35), and the fact that it was not ob- hood threshold of ten. Of the 335 sources detected by SBK2009, served in any XMM-Newton observation taken before 2004 was 304 sources are also contained in the XMM LP-total catalogue, already reported by Trudolyubov & Priedhorsky (2004). The i.e. 31 sources are not detected. Of the 304 re-detected sources, source was first detected with XMM-Newton in the observation two ([SBK2009] 298, 233) are found with a detection likeli- from 31 December 2006. hood below ten. Of the 31 undetected sources, 27 were also not detected in PFH2005. The remaining four sources correlate with PFH2005 sources, which were not detected in the present 7.3. ROSAT catalogues study. SBK2009 state that they find 34 sources not present in the Of the 86 sources detected with ROSAT HRI in the central ∼34 source catalogue of PFH2005. A possible reason for this may of M 31 (PFJ93), all but eight sources ([PFJ93] 1, 2, 31, 33, 40, ff be that SBK2009 used di erent energy bands for source detec- 48, 63, 85) are detected in the XMM-Newton observations. Six tion. They also had five bands, but they combined bands 2 and 3 of these eight sources ([PFJ93] 1, 2, 31, 33, 63, 85) have already from PFH2005 into one band in the range 0.5–2 keV, and on the been discussed in PFH2005 and classified as transients. Sources other hand they split band 5 of PFH2005 into two bands from [PFJ93] 40 and 48 correlate with [PFH2005] 312 and 332, re- 4.5–7 keV and from 7–12 keV, respectively. This might also ex- spectively, which are discussed in Sect. 7.1. In addition to these plain why most of the additional found sources were classified eight sources, PFH2005 did not detect source [PFJ93] 51. This as hard . source was detected in the XMM-Newton observations centred Orio (2006) addressed the population of SSSs and QSSs on RX J0042.6+4115 and was thus classified as a recurrent tran- based on the same archival observations as PFH2005. Orio sient (see SPH2008). (2006) detected 15 SSSs, 18 QSSs and ten SNRs of which In each of the two ROSAT PSPC surveys of M 31, 396 in- one ([O2006] Table 4, Src. 3) is also listed as an SSS ([O2006] dividual X-ray sources were detected (SHP97 and SHL2001). Table 2, Src. 13). Of these sources two SSSs, four QSSs and two From the SHP97 catalogue 130 sources were not detected. SNRs (among them is the source [O2006] Table 4, Src. 3) are not Of these sources 48 are located outside the FoV of our contained in the XMM LP-total catalogue. These seven sources XMM-Newton M 31 survey. From the SHL2001 catalogue, are also not present in the PFH2005 catalogue. 93 sources are not detected, 60 of which lie outside the XMM- The nine bright variable sources from Osborne et al. (2001) Newton FoV.For information on individual sources see Table 13. were all detected. Forty-four (out of 302) sources from SHP97 and 27 (out of 293) sources from SHL2001, have ROSAT detection likelihoods 7.2. Chandra catalogues higher than 15, but are not listed in the XMM LP-total catalogue. These sources have to be regarded as transient or at least highly The Chandra catalogues used for cross-correlations were pre- variable. sented in Sect. 1 (see also Table 4). Details of the comparison between the XMM LP-total cat- 18 The source was observed with XMM-Newton on 11 January 2001. alogue and the different Chandra catalogues can be found Obs. id.: 0065770101.

A55, page 17 of 51 A&A 534, A55 (2011)

Table 12. Sources detected in previous Chandra studies that are not present in the XMM LP-total catalogue.

Kong et al. (2002b) 204 sources 58 not detected 5 transient: r3-46, r3-43, r2-28, r1-23, r1-19 20 variable: r3-53, r3-77, r3-106, r3-76, r2-52, r2-31, r2-23, r1-31, r2-20, r1-24, r1-28, r1-27, r1-33, r1-21, r1-20, r1-7, r2-15, r1-17, r1-16, r2-47 33 unclassiﬁed: r3-102, r3-92, r3-51, r3-75, r3-91, r3-89, r3-101, r3-88, r2-44, r2-55, r2-54, r3-32, r2-53, r1-30, r3-99, r1-22, r1-26, r1-18, r3-26, r2-41, r2-40, r3-71, r2-50, r2-49, r2-38, r3-97, r2-46, r3-12, r3-66, r3-104, r3-82, r3-5, r3-4

Kaaret (2002) 142 sources 26 not detected 3 transient: J004217.0+411508, J004243.8+411604, J004245.9+411619 7 variable: J004232.7+411311, J004242.0+411532, J004243.1+411640, J004244.3+411605, J004245.2+411611, J004245.5+411608, J004248.6+411624 16 unclassiﬁed: J004207.3+410443, J004229.1+412857, J004239.5+411614, J004239.6+411700, J004242.5+411659, J004242.7+411503, J004243.1+411604, J004244.2+411614, J004245.0+411523, J004246.1+411543, J004247.4+411507, J004249.1+411742, J004251.2+411639, J004252.3+411734, J004252.5+411328, J004318.5+410950

Williams et al. (2004) 166 sources 28 not detected 12 transient: s1-79, s1-80, s1-82, r3-46, r2-28, r1-23, r1-19, r2-69, r1-28, r1-35, r1-34, n1-85 7 variable: r2-31, r1-31, r1-24, r1-20, r1-7, r1-17, r1-16 9 unclassiﬁed: s1-81, r2-68, s1-85, r1-30, r1-22, r1-26, r1-18, n1-77, n1-84

Voss & Gilfanov (2007) 261 sources 104 not detected 11 transient: 6, 12, 29, 32, 41, 51, 59, 84, 118, 130, 146 15 variable: 3, 5, 8, 9, 18, 22, 24, 27, 44, 63, 92, 96, 99, 149, 169 78 unclassiﬁed: 4, 19, 21, 25, 26, 30, 37, 39, 40, 42, 48, 49, 53, 56, 57, 58, 60, 62, 65, 70, 73, 75, 76, 77, 80, 82, 84, 86, 87, 89, 91, 94, 97, 98, 104, 109, 114, 115, 117, 119, 122, 124, 129, 133, 138, 141, 143, 144, 145, 150, 152, 158, 162, 164, 167, 171, 173, 182, 183, 188, 189, 191, 193, 194, 197, 202, 205, 206, 210, 213, 217, 219, 220, 225, 256, 257, 263

Williams et al. (2006b) 45 sources 25 not detected 25 transient: n1-26, n1-85, n1-86, n1-88, n1-89, r1-19, r1-23, r1-28, r1-34, r1-35, r2-28, r2-61, r2-62, r2-66, r2-69, r2-72, r3-43, r3-46, s1-18, s1-27, s1-69, s1-79, s1-80, s1-82, s2-62

DKG2004 43 sources 15 not detected 9 transient: s2-62, s1-27, s1-69, s1-18, n1-26, r2-62, r1-35, r2-61, r2-66 5 unclassiﬁed: s2-27, s2-10, n1-29, n1-46, r2-54 1 not in FoV: n1-66

Di Stefano et al. (2002) 28 sources two not detcted 2 unclassiﬁed: 17 (= ˆ r2-15), 28 (= ˆ r3-71)

Notes. Variability information (transient, variable) is taken from the papers. “Unclassiﬁed” denotes sources which are not indicated as transient or variable sources in the papers.

7.4. Einstein catalogue Sect. 7.1. Apart from [TF91] 106, which is suggested as a possible faint transient by SHL2001, the remaining 18 sources are The list of Einstein X-ray sources in the field of M 31 re- also not detected by PFH2005. They classified those sources as ported by TF91 contains 108 sources, with 81 sources taken transient. from the Einstein HRI data with an assumed positional error of 3 (reported by Crampton et al. 1984), and 27 sources based 8. Cross-correlations with catalogues on Einstein IPC data with a 45 positional error. Applying at other wavelengths the above mentioned correlation procedure to the Einstein HRI sources, 64 of these sources are also detected in this work The XMM LP-total catalogue was correlated with the catalogues and listed in the XMM LP-total catalogue, i.e. 17 sources are and public data bases given in Sect. 3.8. Two sources (from the not detected ([TF91] 29, 31, 35, 39, 40, 43, 46, 50, 53, 54, 65, XMM LP-total and from the reference catalogues) were be con- 66, 72, 75, 78, 93, 96). For the Einstein IPC sources only the sidered as correlating, if their positions matched within the un- 1σ positional error was used to search for counterparts among certainty (see Eq. (4)). the XMM-Newton sources. Of the 27 Einstein IPC sources six However, the correlation of an X-ray source with a source remain without a counterpart in our catalogue ([TF91] 15, 99, from the reference catalogue does not necessarily imply that the 100, 106, 107, 108), of which [TF91] 15 and 108 are located two sources are counterparts. To confirm this, additional infor- outside the field of M 31 covered by the XMM LP-total cata- mation is needed, such as corresponding temporal variability of logue. Sources [TF91] 50 and 54 correlate with [PFH2005] 312 both sources or corresponding spectral properties. We should and 316, respectively. Both sources were already discussed in also take into account the possibility that the counterpart of the

A55, page 18 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 13. Sources from the ROSAT PSPC catalogues that are not present in the XMM LP-total catalogue.

SHP97 396 sources 130 not detected 48 outside FoV: 1, 2, 3, 4, 5, 7, 8, 14, 31, 41, 72, 91, 98, 104, 120, 125, 159, 202, 209, 271, 276, 285, 286, 290, 300, 312, 314, 320, 342, 350, 363, 367, 371, 374, 383, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396 1 transient: 69 21 not detected, LH < 12: 19, 24, 27, 33, 46, 52, 59, 63, 68, 71, 133, 149, 161, 264, 273, 275, 307, 329, 330, 358, 377 16 not detected, 12 ≤ LH < 15: 12, 15, 49, 82, 93, 113, 114, 128, 196, 230, 262, 283, 334, 364, 372, 376 44 not detected, LH ≥ 15: 16(LH = 26.6), 32(30.2), 43(18.2), 45(51.2), 60(20.1), 66(36.2), 67(4536.2), 78(20.5), 80(16.3), 81(26.6), 88(33.7), 95(548.0), 102(16.4), 126(217.3), 141(843.3), 145(46.9), 146(673.7), 166(17.4), 167(90.0), 171(54.3), 182(454.4), 186(39.8), 190(113.0), 191(54.5), 192(54.3), 203(103.3), 214(400.2), 215(251.0), 232(104.4), 245(26.0), 260(54.6), 263(38.1), 265(24.6), 268(54.3), 270(40.4), 277(15.6), 309(81.8), 319(23.4), 331(19.5), 335(51.2), 340(27.5), 341(28.1), 365(22.4), 373(69.5) SHL2001 396 sources 93 not detected 60 outside FoV: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 21, 22, 32, 39, 58, 67, 69, 75, 77, 81, 83, 85, 90, 93, 125, 141, 146, 160, 164, 192, 202, 243, 260, 282, 296, 298, 302, 325, 326, 328, 355, 371, 372, 378, 379, 383, 388, 389, 390, 391, 392, 393, 394, 395, 396 4 not detected, LH < 12: 62, 96, 238, 269 2 not detected, 12 ≤ LH < 15: 231, 361 27 not detected, LH ≥ 15: 51(LH = 28.4), 104(901.2), 121(94.1), 126(46.2), 143(34.7), 168(131.9), 171(43.0), 173(317.8), 190(215.8), 207(98.0), 208(298.8), 226(73.1), 230(75.6), 232(1165.6), 240(218.4), 246(39.9), 248(219.6), 256(60.0), 267(22.2), 271(52.8), 322(2703.3), 324(147.7), 344(40.7), 356(15.3), 365(19.0), 380(17.4), 384(15.8) examined X-ray source is not even listed in the reference cata- was done e.g. in PFH2005). Therefore the source classification, logue used (due to faintness for example). and thus the correlation selection process, is based on the cross The whole correlation process will get even more challeng- correlations between the different reference catalogues, on the ing if an X-ray source correlates with more than one source from X-ray properties (hardness ratios, extent and time variability), the reference catalogue. In this case we need a method to de- and on the criteria given in Table 6. For reasons of completeness cide which of the correlating sources is the most likely to cor- we give for each X-ray source the number of correlations found respond to the X-ray source in question. Therefore, the method in the USNO-B1, 2MASS and LGGS catalogues in Table 5. The used should indicate how likely the correlation is with each one caveat of this method is that it cannot quantify the probability of of the sources from the reference catalogue. Based on these like- the individual correlations. lihoods one can define criteria to accept a source from the reference catalogue as being the most likely source to correspond to the X-ray source. 9. Foreground stars and background objects The simplest method uses the spatial distance between the 9.1. Foreground stars X-ray source and the reference sources to derive the likelihoods. In other words, the source from the reference catalogue that is X-ray emission has been detected from many late-type – spec- located closest to the X-ray source is regarded as the most likely tral types F, G, K, and M – stars, as well as from hot source corresponding to the X-ray source. OB stars (see review by Schmitt 2000). Hence, X-ray obser- An improved method is a “likelihood ratio” technique, were vations of nearby galaxies also reveal a significant fraction of an additional source property (e.g. an optical magnitude in deep Galactic stars. With typical absorption-corrected luminosities of 31 −1 field studies) is used to strengthen the correlation selection pro- L0.2−10 keV < 10 erg s , single stars in other galaxies are too cess. This technique was applied successfully to deep fields to faint to be detected with present instruments. However, concen- find optical counterparts of X-ray sources (e.g. Brusa et al. trations of stars can be detected, but not resolved. 2007). A drawback of this method is that one a priori has to Foreground stars (fg Stars) are a class of X-ray sources know the expected probability distribution of the optical magni- which are homogeneously distributed over the field of M 31 tudes of the sources belonging to the studied object. In our case, (Fig. 10). The good positional accuracy of XMM-Newton and this means that we have to know the distribution function for all the available catalogues USNO-B1, 2MASS and LGGS allow optical sources of M 31 that can have X-ray counterparts, with- us to efficiently select this type of source. The selection crite- out including foreground and background sources. Apart from ria are given in Table 6. The optical follow-up observations of the fact that such distribution functions are unknown, an addi- Hatzidimitriou et al. (2006)andBonfini et al. (2009) have con- tional challenge would be the time dependence of the magnitude firmed the foreground star nature of bright foreground star candi- of the optical sources (e.g. of novae) and of the connection be- dates selected in PFH2005, based on the same selection criteria tween optical and X-ray sources (e.g. optical novae and SSSs). as used in this paper. Somewhat different criteria were applied Therefore it is not possible to apply this “likelihood ratio” tech- for very red foreground stars, with an LGGS colour V − R > 1 nique to the sources in the XMM LP-total survey. The whole or USNO-B1 colour B2 − R2 > 1. These are classified as fore- correlation selection process becomes even more challenging if ground star candidates, if fx/ fopt < −0.65 and fx/ fopt,R < −1.0. more than one reference catalogue is used. A misclassification of symbiotic systems in M 31 as foreground To be able to take all available information into account, we objects by this criterion can be excluded, as symbiotic systems decided not to automate the selection process, but to select the typically have X-ray luminosities below 1033 erg s−1,whichis class and most likely correlations for each source by hand (as it more than a factor 100 below the detection limit of our survey.

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Table 14. Infrared colours and spectral types of foreground stars that show ﬂares.

No. J mag H mag K mag SpT∗ err+ 473 12.984 12.681 12.558 K0 0.4 714 14.310 13.618 13.458 M0 0.2 780 14.251 13.595 13.351 M3 0.1 1551 12.666 12.009 11.806 M2 0.1 1585 13.488 12.899 12.650 M2 0.1 1676 10.460 9.878 9.798 K1 0.2 1742 13.722 13.138 12.896 M1 0.2

Notes. (∗) Spectral type; (+) error (in subtypes).

as “foreground star candidates” in the comment column of Table 5. Six sources (No. 473, No. 780, No. 1551, No. 1585, No. 1676, No. 1742), classified as foreground star candidates, have X-ray light curves that in a binning of 1000 s showed flares (see Fig. 11). These observations strengthen the foreground star classification. A seventh source (No. 714) is classified as a foreground star candidate, since its hardness ratios and its fx/ fopt ratio in the quiescent state fulfil the selection criteria of foreground star candidates. In addition, the source shows a flare throughout observation ss3. Hence, the fx/ fopt ratio for this observation, in 15 arcmin which the source is brightest, is too high to be consistent with the range of values expected for foreground stars. Table 14 gives the J, H and K magnitudes taken from the 2MASS catalogue for each of the six flaring foreground stars. Fig. 10. The spatial distribution of foreground stars and candidates, clas- Using the standard calibration of spectral types for dwarf stars sified in the XMM LP-total catalogue. The image shows the homoge- based on their near infrared colours (from the fourth edition of neous distribution of the sources over the covered field (marked with Allen’s astrophysical quantities, ed. Cox, p. 151) we derived the green dots). spectral classification for the objects, using both H−K and J−K. The spectral types (and “error”) we give in Table 14 are derived from averaging the two classes (derived from the two colours). If the foreground star candidate lies within the field cov- The spectral types are entirely consistent with those expected for ered by the LGGS we checked its presence in the LGGS im- flare stars (usually K and M types). ages (as the LGGS catalogue itself does not list bright stars, Figure 12 shows the XID flux distribution for foreground because of saturation problems). Otherwise DSS2 images were stars and foreground star candidates, which ranges from − − − − − − used. Correlations with bright optical sources from the USNO- 6.9 × 10 16 erg cm 2 s 1 to 2.0 × 10 13 erg cm 2 s 1. Most of the B1 catalogue, with an f / f in the range expected for fore- foreground stars and candidates (257 sources) have fluxes below x opt − − − ground stars, that were not visible in the optical images were 5 × 10 14 erg cm 2 s 1. rejected as spurious. We found 223 foreground star candidates. Fourty sources were identified as foreground stars, either be- 9.1.1. Comparing XMM-Newton, Chandra and ROSAT cause they are listed in the globular cluster catalogues as spec- catalogues troscopically confirmed foreground stars or because they have a spectral type assigned to them in the literature (Bonfini et al. In the combined ROSAT PSPC survey (SHP97, SHL2001) 2009; Hatzidimitriou et al. 2006, SIMBAD). 55 sources were classified as foreground stars. Of these, Two of the foreground star candidates close to the centre of 14 sources remain without counterparts in the present XMM- M 31 (No. 826, No. 1110) have no entry in the USNO-B1 and Newton survey. Five of these 14 sources are located outside LGGS catalogues, and one has no entry in the USNO-B1 R2 the field observed with XMM-Newton. Forty-one ROSAT fore- and B2 columns (No. 976). However, they are clearly visible on ground star candidates have counterparts in the XMM LP-total LGGS images, they are 2MASS sources and they fulfil the X- catalogue. Of these counterparts, 16 were classified as fore- ray hardness ratio selection criteria. Therefore, we also classify ground star candidates and four were identified as foreground them as foreground stars. stars (spectral type from Bonfini et al. 2009; Hatzidimitriou et al. The following 19 sources were selected as very red fore- 2006, or SIMBAD). In addition 12 sources were listed as hard , ground star candidates: No. 54, No. 118, No. 384, No. 391, two as AGN candidates and one as a globular cluster candi- No. 393, No. 585, No. 646, No. 651, No. 711, No. 1038, date in the XMM LP-total catalogue. The counterparts of three No. 1119, No. 1330, No. 1396, No. 1429, No. 1506, No. 1605, ROSAT sources remain without classification in the XMM LP- No. 1695, No. 1713 and No. 1747. A further 10 sources total catalogue. (No. 210, No. 269, No. 278, No. 310, No. 484, No. 714, No. 978, Another three ROSAT sources have more than one coun- No. 1591, No. 1908 and No. 1930) fulfil the hardness ratio terpart in the XMM-Newton data. Source [SHP97] 109 corre- criteria, but violate the fx/ fopt criteria and are therefore marked lates with sources No. 597, No. 604, No. 606, and No. 645.

A55, page 20 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31 0.01 −3 counts/s counts/s 05×10 4 4 4 4 4 10 2×10 3×10 4×10 5×10 0 0.01 0.02 0.03 0.04 0104 2×104 3×104 4×104 5×104 6×104 Time (s) Time (s) (a) No. 473 (b) No. 780 0.01 0.015 counts/s counts/s −3 0.02 0.03 0.04 0.05 5×10

0104 2×104 3×104 4×104 Time (s) 0104 2×104 3×104 4×104 (c) No. 1551 Time (s) (d) No. 1585 counts/s counts/s 0 0.01 0.02 0.03 0.04

0.02 0.044 0.064 0.08 4 4 0102×10 3×10 4×10 4 4 4 4 Time (s) 10 2×10 3×10 4×10 (e) No. 1676 Time (s) (f) No. 1742 counts/s 0 0.01 0.02 0.03 2×104 3×104 4×104 5×104 6×104 Time (s) (g) No. 714

Fig. 11. X-ray light curves of foreground stars and candidates that, with a binning of 1000 s, show ﬂares.

A55, page 21 of 51 A&A 534, A55 (2011)

candidates by our XMM-Newton study (cf. Table 5). For source No. 696 (= ˆ s1-20) Hatzidimitriou et al. (2006) obtained the spectral type G0. Of the four sources listed as foreground stars in Vo ss & Gilfanov (2007) only one source (No. 936= ˆ [VG2007] 168) was confirmed as a foreground star, based on the entry in the RBC V3.5 and Caldwell et al. (2009). The second source (No. 1118= ˆ [VG2007] 180) is listed in the RBC V3.5 and Caldwell et al. (2009) as a globular cluster. The third source (No. 829= ˆ [VG2007] 181) does not have a counterpart in the USNO-B1, 2MASS or LGGS catalogues, nor does it fulfil the hardness ratio criteria for foreground stars. Hence, the source is classified as hard . The fourth source ([VG2007] 81) is not spatially resolved from its neighbouring source [VG2007] 79 in our XMM-Newton observations (source No. 1078). Hence source No. 1078 is classified as hard .

9.2. Galaxies, galaxy clusters and AGN The majority of background sources belong to the class of active galactic nuclei (AGN). This was shown by the recent deep- Fig. 12. Distribution of the source fluxes in the 0.2–4.5 keV (XID) band. est available surveys of the X-ray background (Mushotzky et al. The diagram shows a histogram of the number of foreground stars and 2000; Hasinger et al. 2001; Brandt & Hasinger 2005). The class candidates per flux bin, in logarithmic scales. of AGN is divided into many sub-sets. The common factor in all the sub-sets is that their emission emanates from a small, spatially unresolved galactic core. The small size of the emit- The former three are classified as hard , while source ting region is implied by the X-ray flux variability observed in No. 645 is classified as a foreground star candidate. However many AGN, which is on time scales as short as several minutes source No. 645 has the largest distance from the position of (to years). The observed X-ray luminosities range from 1039 to [SHP97] 109 compared to the other three XMM-Newton coun- 1046 erg s−1, sometimes even exceeding 1046 erg s−1. Although terparts. Furthermore, this source had a flux below the ROSAT AGN show many different properties, such as the amount of ra- detection threshold (about a factor 2.6) in the XMM-Newton ob- dio emission or the emission line strengths and widths, they are servations and is about a factor 3–34 fainter than the three other believed to be only different facets of one underlying basic phe- possible XMM-Newton counterparts. Thus it is very unlikely that nomenon (cf. Urry & Padovani 1995): the accretion of galac- 6 9 [SHP97] 109 represents the X-ray emission of a foreground star. tic matter onto a supermassive black hole (∼10 −10 M )inthe Source [SHL2001] 156 has two XMM-Newton counter- centre of the galaxy. parts and is discussed in Sect. 10.1.3. The third source It is difficult and, to some extent, arbitrary to distinguish be- ([SHL2001] 374) correlates with sources No. 1922 and tween active and normal galaxies, since most galaxies are be- No. 1924. The two XMM-Newton sources are classified as hard lieved to host a black hole at the position of their kinetic centre and as a foreground star candidate, respectively. In the source (Bender et al. 2005). In normal galaxies the accretion rate to the catalogue of SHL2001 source [SHP97] 369 is listed as the coun- central supermassive BH is so low, that only weak activity can be terpart of [SHL2001] 374. The source in the first ROSAT survey detected – if at all. The overall thermal emission of the nuclear has a smaller positional error and only correlates with source region is due to bremsstrahlung from hot gas. The total X-ray No. 1924. Although this seems to indicate that source No. 1924 luminosity of a normal galaxy can reach some 1041 erg s−1,at is the counterpart of [SHL2001] 374, we cannot exclude the pos- most. It consists of diffuse emission and emission of unresolved sibility that [SHL2001] 374 is a blend of both XMM-Newton individual sources. sources, as these two sources have similar luminosities in the Galaxy clusters (GCls) are by far the largest and most mas- XMM-Newton observations. sive virialised objects in the Universe. Their masses lie in the 14 15 Kong et al. (2002b) classified four sources as foreground range of 10 –10 M and they have sizes of a few mega- stars. For two sources (No. 960= ˆ r2-42 and No. 976= ˆ r3- parsecs (Mpc). A mass-to-light ratio of M/L 200 M /L in- 33) the classification is confirmed by our study. The third dicates that galaxy clusters are clearly dominated by their dark source (No. 1000= ˆ r2-19) remained without classification in the matter content. Furthermore, galaxy clusters allow us to study XMM LP-total catalogue, as it is too soft to be classified as the baryonic matter component, as they define the only large and the optical counterpart found in the LGGS catalogue volumes in the Universe from which the majority of baryons does not fulfil the fx/ fopt criteria. The fourth source (r2-46) was emit detectable radiation. This baryonic gas, the hot intraclus- not detected in the XMM-Newton observations. ter medium (ICM), is extremely thin, with electron densities of 2 5 −3 The foreground star classification of three sources (s1-74, ne 10 –10 m , and fills the entire cluster volume. Owing s1-45, n1-82) in Williams et al. (2004) is confirmed by the to the plasma temperatures of kB T 2–10 keV, the thermal 43 XMM LP-total study (No. 289, No. 603, No. 1449). For source ICM emission gives rise to X-ray luminosities of LX 10 – No. 289 the spectral type F0 was determined (Hatzidimitriou 3 × 1045 erg s−1. Therefore galaxy clusters are the most X-ray et al. 2006). luminous objects in the Universe next to AGN. The source list of DKG2004 contains six sources (s2-46, We identified four sources as background galaxies and 11 s2-29, s2-37, s1-45, s1-20, r3-122) that are classified as fore- as AGN, and classified 19 galaxy and 49 AGN candidates. The ground stars. All six sources are confirmed as foreground star classification is based on SIMBAD and NED correlations and

A55, page 22 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31 correlations with sources listed as background objects in the globular cluster catalogues (RBC V3.5 and Caldwell et al. 2009). Sources are classified as AGN candidates, if they have a radio counterpart (NVSS; Braun 1990; Gelfand et al. 2004) with the additional condition of being neither a SNR nor a SNR candidate from X-ray hardness ratios, as well as not being listed as a “normal” background galaxy in Gelfand et al. (2004). Most AGN will be classified as hard ((HR2−EHR2) > −0.2, see Table 6) because of their intrinsic power law component. Additional absorption in the line of sight by the interstellar medium of M 31 will lead to an even higher HR2. Only the few AGN with a dom- inant component in the measured flux below 1 keV may lead to a classification SNR or fg Star in our adapted scheme. One (No. 995) of the four identified galaxies is M 32. An overview of previous X-ray observations of this galaxy is given in PFH2005. They also discuss the fact that Chandra resolved the X-ray emission of M 32 into several distinct point sources (maximum separation of the three central Chandra sources 8. 3). Although M 32 is located closer to the centre of the FoV in the observations of field SS1, than it was in the s1 observation used in PFH2005, XMM-Newton still detects only one source. The remaining three sources (No. 88, No. 403, No. 718) are identified as galaxies, because they are listed as background galaxies in both the RBC V3.5 and Caldwell et al. (2009). For source No. 403 (B 007) NED gives a redshift of 0.139692 ± 0.000230 (Kim et al. 2007). Eleven X-ray sources are identified as AGN. The first one 15 arcmin (No. 363) correlates with a BL Lac object located behind M 31 (NED, see also PFH2005). The second source (No. 745) correlates with a Seyfert 1 galaxy (5C 3.100), which has a redshift of ≈0.07 (SIMBAD). The third source (No. 1559) correlates Fig. 13. The spatial distribution of background sources and candidates, with a quasar (Sharov 21) that showed a single strong optical ∼ classified in the XMM LP-total catalogue. AGN are marked with blue flare, during which its UV flux has increased by a factor of 20 dots, “normal” galaxies with red dots and galaxy clusters with green (Meusinger et al. 2010). The remaining sources were spectro- dots. scopically confirmed (from our optical follow-up observations) to be AGN (D. Hatzidimitriou, priv. comm.; and Hatzidimitriou Table 15. Spectral fit parameters for extended sources. et al. 2010, in prep.). In Sect. 5.4 the 12 extended sources in the XMM LP-total / 21 −2 / χ2/ catalogue were presented. Kotov et al. (2006) showed that the Src ID NH 10 cm kBT keV redshift d.o.f. . +1.63 . +2.30 . +1.24 / brightest of these sources (No. 1795) is a galaxy cluster located 141 1 19−0.88 2 17−0.68 0 24−0.11 78.5 53 z = . . +1.16 . +0.64 . +0.15 / at a redshift of 0 29. For the remaining 11 sources, X-ray 252 0 61−0.43 1 95−0.29 0 22−0.07 56.4 151 spectra were created and fitted with the MEKAL model in XSPEC. 304 2.68+2.64 0.95+3.32 0.12+0.07 50.9/57 Unfortunately, for most of the examined sources the spectral pa- −1.85 −1.95 −0.05 1543 2.74+6.91 2.08+2.31 0.61+1.11 32.9/34 rameters (foreground absorption, temperature and redshift) are −1.76 −1.11 −0.26 not very well constrained. Nevertheless four sources (No. 141, No. 252, No. 304, No. 1543) with temperatures in the range of field. However, in the fields located along the major axis of ∼1–2 keV and proposed redshifts between 0.1–0.6 were found M 31 we mainly see AGN, which are bright enough to be visible (Table 15). Inspection of optical images (DSS 2 images and if through M 31, while most of the galaxies and galaxy clusters are available LGGS images) revealed an agglomeration of optical detected in the outer fields. sources at the positions of these four extended X-ray sources. Thus they are classified as galaxy cluster candidates. 9.2.1. Comparing XMM-Newton, Chandra and ROSAT Although, B242 (the optical counterpart of source No. 304) is listed as a globular cluster candidate in the RBC3.5 catalogue, catalogues Caldwell et al. (2009) classified this source as a background ob- Of the ten ROSAT PSPC survey sources classified as back- ject. Our findings from the X-rays favour the background ob- ground galaxies one is located outside the field of the Deep ject classification. Hence a globular cluster classification for this XMM-Newton Survey. The remaining objects are confirmed to source seems to be excluded. be background sources and are classified or identified as galax- Source No. 1912 was already classified as a galaxy clus- ies or AGN. The only case which is worth discussing in more ter candidate in PFH2005. The spectrum confirms this classi- detail is the source pair [SHP97] 246 and [SHL2001] 252. From = . +0.53 × 21 −2 fication. The best fit parameters are NH 1 29−0.41 10 cm , the XMM-Newton observations it is evident that this source pair = . +0.8 . +0.03 T 2 8−0.5 keV and redshift of 0 06−0.04. is not one source, as indicated in the combined ROSAT PSPC A plot of the spatial distribution of the classified/identified source catalogue (SHL2001), but consists of three individual background sources is given in Fig. 13, which shows that these sources (No. 1269, No. 1279 and No. 1280). [SHL2001] 252 sources are rather homogeneously distributed over the observed correlates spatially with all three XMM-Newton sources, while

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[SHP97] 246 correlates only with source No. 1269, which is identified as a foreground star of type K2 (SIMBAD). The two other XMM-Newton counterparts of [SHL2001] 252 are classified as a galaxy candidate and an AGN candidate, respectively. In summary, [SHL2001] 252 is most likely a blend of both background sources and maybe even a blend of all three XMM- Newton sources, while [SHP97] 246 seems to be the X-ray counterpart of the foreground star mentioned above. Kong et al. (2002b) classified source r3-83 (No. 1132) as an extragalactic object, as it is listed in SIMBAD and NED as an emission line object. Following PFH2005, we classified source No. 1132 as hard . The BL Lac object (No. 363) was also detected in Chandra observations (Williams et al. 2004).

10. M 31 sources 10.1. Supersoft sources Supersoft source (SSS) classification is assigned to sources showing extremely soft spectra with equivalent blackbody temperatures of ∼15–80 eV. The associated bolometric luminosities are in the range of 1036–1038 erg s−1 (Kahabka & van den Heuvel 1997). Because of the phenomenological definition, this class is likely to include objects of several types. The favoured model for these sources is that they are close binary systems with a 15 arcmin white dwarf (WD) primary, burning hydrogen on the surface (cf. Kahabka & van den Heuvel 1997). Close binary SSSs include post-outburst, recurrent, and classical novae, the hottest symbiotic stars, and other LMXBs containing a WD (cataclysmic variables, CVs). Symbiotic systems, which contain a WD in a Fig. 14. The spatial distribution of SSSs classified in the XMM LP-total wide binary system, may also be observed as SSSs (Kahabka catalogue. The positions of the SSSs are marked with red and green & van den Heuvel 1997). Because matter that is burned can be dots. Sources that correlate with optical novae are given in green. An retained by the WD, some SSS binaries may be progenitors of enhancement of sources in the central field is clearly visible. type-Ia supernovae (cf. van den Heuvel et al. 1992). The XMM LP-total catalogue contains 30 SSS candidates would lead to increased unabsorbed luminosities. We also have that were selected on the basis of their hardness ratios (see Fig. 6 to take into account that we might have observed the source dur- and Table 6). ing a phase of rising or decaying luminosity, i.e. not at maximum luminosity. 10.1.1. Spatial and flux distribution Figure 14 shows the spatial distribution of the SSSs. Clearly 10.1.2. Correlations with optical novae visible is a concentration of sources in the central field. There By cross-correlating with the nova catalogue19 indicated in are two explanations for that central enhancement. The first is Sect. 3.8, 14 of the 30 SSSs can be classified as X-ray coun- that the central region was observed more often than the remain- terparts of optical novae. Of these 14 novae, eight (No. 748, ing fields and therefore there is a higher chance of catching a No. 993, No. 1006, No. 1046, No. 1051, No. 1076, No. 1100, transient SSS in outburst. The second reason is that the major and No. 1236) are already discussed in PFF2005 and PHS2007. class of SSSs in the centre of M 31 are optical novae (PFF2005, Nova M31N 2001-11a was first detected as a supersoft X-ray PHS2007). Optical novae are part of the old stellar population source. Motivated by that SSS detection, Smirnova et al. (2006) which is much denser in the centre of M 31. found an optical nova at the position of the SSS in archival Figure 15 gives the distribution of 0.2–1.0 keV source fluxes optical plates which had been overlooked in previous nova for all SSSs (black) and for those correlating with optical no- searches. Nova M31N 2007-06b has been discussed in Henze vae (blue). The unabsorbed fluxes were determined assuming et al. (2009a). The remaining four novae are discussed individu- a 50 eV blackbody model (PFF2005). The two brightest SSSs ally in more detail below. > −12 −2 −1 (FX 10 erg cm s ) consist of a persistent source with As was shown in the XMM-Newton/Chandra M31nova 217 s pulsations (No. 1061; Trudolyubov & Priedhorsky 2008) monitoring project20, it is absolutely necessary to have a homo- and the nova M31N 2001-11a (No. 1416; Smirnova et al. 2006). geneous and dense sample of deep optical and X-ray observa- A large fraction of SSSs are rather faint, with fluxes below tions in order to study optical novae and their connections to su- 5 × 10−14 erg cm−2 s−1. Four sources have absorption-corrected 36 −1 persoft X-ray sources. In the optical, the outer regions of M 31 luminosities below 10 erg s (0.2–1.0 keV), which was indi- are regularly observed down to a limiting magnitude of ∼17 mag cated as the limiting luminosity for SSSs. That does not necessarily imply that these sources are not SSSs, since it is possible 19 http://www.mpe.mpg.de/~m31novae/opt/m31/M31_table. that the blackbody fit chosen does not represent well the proper- html ties of these sources. A higher absorption or a lower temperature 20 http://www.mpe.mpg.de/~m31novae/xray/index.php

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100 90% M31N 1997-10c

36 3•10 80 68% 90% 37 6 0 3 1•1 60 1•10 68% 37 3•10 36 kT (eV) 3•10 68% 38 90% 1•10 40 38 37 3•10 1•10 37 39 3•10 1•10 H 38 1•10 1•1040 38 3•10 39 1•10 90% 20 40 41 1•10 1•10 Foreground N

0.0 0.8 1.6 2.4 3.2 4.0 21 -2 NH (10 cm )

Fig. 16. Column density-temperature confidence contours inferred from the fit to the XMM-Newton EPIC PN spectrum of M31N1997-10c. The formal best fit parameters are indicated by the star. Also drawn are lines of constant bolometric luminosity (in erg s−1). The vertical dashed line Fig. 15. Distribution of the source fluxes in the 0.2–1.0 keV band. The indicates the Galactic foreground absorption in the direction of M 31. diagram shows the number of SSSs per flux bin plotted versus the flux in logarithmic scale. The blue histogram gives the distribution of SSSs Table 16. 3σ upper limits for the absorption-corrected luminosities for correlating with optical novae. Nova M31N 1997-10c.

37 −1 Observation LX/10 erg s (0.2–1.0 keV) (Texas Supernova Search (TSS); Quimby 2006), while in X-rays c2 10.8+ only “snapshots” are available. Hence, the correlations of optical c3 1.9 novae with detected SSSs have to be regarded as lucky coinci- c4 1.0 dences. That also means that the identified nova counterparts are detected at a random stage of their SSS evolution which does Notes. (+) The count rate detected in observation c2 gives a luminosity − not allow us to constrain the exact start or end point of the SSS of 2.4 ± 2.8 × 1037 erg s 1, which results in the upper limit given in the phase, nor the maximum luminosity of the SSS. We also can- Table. The fact that this upper limit is higher than the luminosity detected in observation c1 is, at least in part, attributed to the very short not exclude the possibility that some of the SSSs observed in the ff outer parts of M 31 correspond to the supersoft phase of opti- e ective observing time of less than 6000 s. cal novae for which the optical outburst was missed. In the outer regions of M 31, the samples of optical novae and X-ray SSSs are certainly incomplete, due to the rather high luminosity limit limits of the source luminosity can be derived, which are given in the optical monitoring, and the lack of complete monitoring in Table 16. in X-rays, respectively. So one should be cautious in deriving properties of the disc nova population of M 31 from the available data. Nova M31N 2005-01b was discovered on 19 January 2005 at a white light magnitude of 16.3 by Quimby21. An SSS (No. 764) that correlates with the optical nova (distance: 4. 3; 3σ error: Nova M31N 1997-10c was detected on 2 October 1997 at a 5. 5) was found in observation ss2 taken on 8 July 2006, which B-band magnitude of 16.6 (ShA 58; Sharov & Alksnis 1998). is 535 days after the discovery of the optical nova. Due to the An upper limit of 19 mag on 29 September 1997 was reported severe background screening applied to observation ss2, there is by the same authors. They classified this source as a very fast not enough statistics to obtain a spectrum of the X-ray source. To nova. In the XMM-Newton observation c1 (25 June 2000), an get an estimate of the spectral properties of that source we cre- SSS (No. 871), located within ∼1 . 9 of the optical nova, was ated a spectrum in the 0.2–0.8 keV range of the unscreened data. detected. The source was fitted with an absorbed blackbody Although the spectrum was background corrected, we cannot to- model. The formal best fit parameters of the XMM-Newton tally exclude a contribution from background flares. The spec- 21 −2 EPIC PN spectrum are: absorption NH ≈ 3.45 × 10 cm and trum is best fitted by an absorbed blackbody model with an ab- ≈ 21 −2 kBT 41 eV. The unabsorbed luminosity in the 0.2–1 keV band sorption of NH ≈ 1.03 × 10 cm and a blackbody temperature ≈ × 37 −1 is 5.9 10 erg s . Confidence contours for absorption col- of kBT ≈ 45 eV. The unabsorbed 0.2–1 keV luminosity is LX ∼ umn density and blackbody temperature are shown in Fig. 16.In 1.0 × 1037 erg s−1. In another XMM-Newton observation taken the subsequent XMM-Newton observation of that region taken 1073 days after the optical outburst (ss21; 28 December 2007) about half a year later (c2; 27 December 2000) the source is the X-ray source is no longer visible. The 3σ upper limit of the not detected. Although the source position is covered in obser- unabsorbed source luminosity is ∼3.3 × 1035 erg cm−2 s−1 in the vations c3 (29 June 2001), c4 (6/7 January 2002) and b (16– 0.2–4.5 keV band, assuming the spectral model used for source 19 July 2004) the source was not re-detected. Using the count detection. rates derived for the variability study (see Sect. 6) and assuming the same spectrum for the source as in observation c1, upper 21 http://www.supernovae.net/sn2005/novae.html

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Fig. 17. XMM-Newton EPIC spectrum of nova M31N 2005-01c. The absorbed black body fit to the data is shown in the upper panel. Fig. 18. Column density (NH) – temperature (kBT) confidence contours inferred from the blackbody fit to the XMM-Newton EPIC spectrum of M31N 2005-01c (see Fig. 17). The formal best fit parameters are indi- Nova M31N 2005-01c was discovered on 29 January 2005 at a cated by the star. Also drawn are lines of constant bolometric luminosity white light magnitude of 16.1 by Quimby22.IntheXMM-Newton and the vertical dashed line indicates the Galactic foreground absorption observation from 02 January 2007 (ns2, 703 days after optical (see Fig. 16). outburst) an SSS was detected (No. 1675) at a position consistent with that of the optical nova (distance: 0. 9). The X-ray spectrum (Fig. 17) can be well fitted by an absorbed blackbody 10.2. Supernova remnants model with the following best fit parameters: absorption NH = 1.58+0.65 × 1021 cm−2 and k T = 40 ± 6 eV. The unabsorbed After an supernova explosion the interaction between the ejected −0.45 B material and the ISM forms a supernova remnant (SNR). 0.2–1 keV luminosity is L ∼ 1.2 × 1038 erg s−1. Confidence X The SNR X-ray luminosities typically vary between 1035 and contours for absorption column density and blackbody tempera- − 1037 erg s 1 (0.2–10keV). ture are shown in Fig. 18. SNRs can be divided into two categories, (i) sources where the thermal components dominate the X-ray spectrum below Nova M31N 2005-09b was discovered in optical images taken 2 keV; and (ii) the so-called “plerions” or Crab-like SNRs with on 01 and 02 September 2005 at white light magnitudes of power law spectra. The former are located in areas of the X-ray ∼18.0 and ∼16.5 respectively. From 31 August 2005, an upper colour/colour diagrams that overlap only with foreground star limit of ∼18.7 mag was reported (Quimby et al. 2005). The nova locii. If we assume that we have identified all foreground star was spectroscopically confirmed (Pietsch et al. 2006) and clas- candidates from the optical correlation and inspection of the op- sified as a possible Fe II or hybrid nova23. An X-ray counter- tical images, the remaining sources can be classified as SNR can- part (No. 92) was detected in the XMM-Newton observation s3 didates using the criteria given in Table 6. Similar criteria were (299 days after the optical outburst). Its position is consistent used to select supernova remnant candidates in XMM-Newton with that of the optical nova (distance: 0. 57). As observation s3 observations of M 33 (Pietsch et al. 2004; Misanovic et al. 2006). was heavily affected by background flares, we only could esti- Ghavamian et al. (2005)andLong et al. (2010) confirmed the mate the spectral parameters from the unscreened data (see also supernova remnant nature of many of these candidates based on paragraph about Nova M31N 2005-01b). A blackbody fit of the optical and radio follow-up observations. They also used a hard- 21 −2 0.2–0.8 keV gives NH ≈ 2.7 × 10 cm , kT ≈ 35 eV, and an un- ness ratio criterion to select supernova remnant candidates from 38 −1 absorbed 0.2–1 keV luminosity of LX ∼ 5.4 × 10 erg s .The Chandra data. X-ray source was no longer visible in observation s31, which An X-ray source is classified as a SNR candidate if it ei- was taken 391 days after observation s3. ther fulfils the hardness ratio criterion given in Table 6 (these are 25 such sources), or if it correlates with a known optical or radio SNR candidate (six sources). The sources assigned the classifi- 10.1.3. Comparing XMM-Newton, Chandra and ROSAT cation of a SNR candidate based on the latter criterion alone, are catalogues marked in the comment column of Table 5 with the flag “only The results and a detailed discussion of a study of the long-term correlation”. As these six SNR candidates would be classified variability of the SSS population of M 31 are presented in Stiele as hard on the basis of their hardness ratios, they are good can- et al. (2010). In summary our comparative study of SSS candi- didates for being “plerions”. SNRs are taken as identified when dates in M 31 detected with ROSAT, Chandra and XMM-Newton they coincide with SNR candidates from the optical or radio and demonstrated that strict selection criteria have to be applied to fulfil the hardness ratio criterion. For a discussion of detection securely select SSSs. It also underlined the high variability of of SNRs in different wavelength bands see Long et al. (2010). the sources in this class and the connection between SSSs and All together, we identified 25 SNRs and 31 SNR candidates in optical novae. the XMM LP-total catalogue. This number is in the range expected from an extrapolation 22 http://www.supernovae.net/sn2005/novae.html of the X-ray detected SNRs in the Milky Way as shown be- 23 http://cfa-www.harvard.edu/iau/CBAT_M31.html low. Assuming that our own Galaxy contains about 1440 X-ray

A55, page 26 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Fig. 20. Hα, R, S II and O III images, taken from the LGG Survey. Over-plotted is a circle at the position of source XMMM31 J003923.5+404419 with a radius of 5. 5(3σ positional error of the X-ray source). The ring-like SNR is clearly visible in the Hα and S II bands.

Fig. 19. Distribution of SNR fluxes in the 0.2–4.5 keV (XID) band. The diagrams show the number of identified and classified SNRs at each flux bin, plotted versus the flux. The distribution for identified SNRs is shown in blue. sources which are brighter than ∼1 × 1035 erg s−1 (Revnivtsev et al. 2006), and that it contains ∼110 SNRs detected in X- rays (Green 2009), we would expect to detect ∼50 SNRs in the XMM LP-total catalogue (0.4× 1897sources − 263fgStars ). This number is in good agreement with the number of identified and classified SNRs. The XID fluxes for SNRs range between 5.9 × 10−14 erg cm−2 s−1 for source No. 1234 and 1.5 × 10−15 erg cm−2 s−1 for source No. 419. These fluxes correspond to luminosities of 4.3 × 1036 erg s−1 to 1.1 × 1035 erg s−1. A diagram of the flux distribution of the detected SNRs and candidates is shown in Fig. 19. Fig. 21. Hα, R, S II and O III images, taken from the LGG Among the 25 identified SNRs, there are 20 SNRs from the Survey. Over-plotted is a circle at the position of source PFH2005 catalogue. Source [PFH2005] 146, which correlates XMMM31 J004413.5+411954 with a radius of 3. 6(3σ positional with the radio source [B90] 11 and the SNR candidate BA146, error of the X-ray source). The SNR “appears as a bright knot”. was not found in the present study. Source [SPH2008] 858, which coincides with a source reported as a ring-like extended object in Chandra observations that was also detected in the opti- radio (Braun 1990) and X-ray (SHP97) range. It was reported as cal and radio wavelength regimes and identified as a SNR (Kong a SNR by SHP97. et al. 2003), was re-detected (No. 1050). Of the 31 SNR candidates ten have been reported by PFH2005. In the following, XMMM31 J004510.5+413251 and XMMM31 J004512.3+ we first discuss in more detail the remaining four identified 420029 (No. 1587 and No. 1593, respectively) are new X-ray SNRs, that appear in the new catalogue but were not included detections and correlate with the radio sources: #354 and #365 in PFH2005: in the list of Braun (1990). Source No. 1587 also correlates with source 37W209 from the catalogue of Walterbos et al. (1985). XMMM31 J003923.5+404419 (No. 182) was classified as a No optical counterparts were reported in the literature. SNR candidate from its [S II]:Hα ratio. It appears as an “irreg- In the following, we discuss two SNR candidates in more ular ring with southerly projection” (Dodorico et al. 1980,and detail: Fig. 20) and correlates with a radio source (Pooley 1969). X-ray radiation of that source was first detected in the present study. XMMM31 J004434.8+412512 (No. 1481) lies in the periphery of a super-shell with [S II]: Hα>0.5(Braun & Walterbos 1993, XMMM31 J004413.5+411954 (No. 1410) was classified as a src 490). Located next to this source is a SNR candidate reported SNR candidate from its [S II]:Hα ratio (Braun & Walterbos in Magnier et al. (1995, src 3-086), which has a radio counterpart 1993; Magnier et al. 1995). From Fig. 21 we can see that the from the NVSS catalogue. No. 1481 also correlates with ROSAT source “appears as a bright knot”, as was already reported by source [SPH97] 284, which was identified as a SNR in SPH97 Braun & Walterbos (1993). The source has counterparts in the due to its spatial correlation with source 3-086. Figure 22 shows

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XMMM31 J004239.8+404318 XMM−Newton, EPIC

284

3-086 0.06

1481 1481 pn FF thin mos1 FF medium

−1 mos2 FF medium 0.04 keV −1

H alpha R band 0.02 Counts s

SII band OIII band

0

1481 1481 0.01

0 Residials −0.01 0.5 1 Channel Energy (keV) Fig. 22. Hα, R, S II and O III images, taken from the LGG Survey. Over-plotted is a blue circle at the position of source Fig. 23. 0.2–3.0 keV EPIC spectrum of source No. 969. The best fit ab- XMMM31 J004434.8+412512 with a radius of 5. 9(3σ positional er- sorbed non-equilibrium ionisation model is indicated by the solid lines. ror of the X-ray source). Source [SPH97] 284 is indicated by a black circle with a radius of 21 (3σ positional error), source 3-086 by the magenta circle with a radius of 10 ; the position of the radio counter- sources are also classified as SNRs or SNR candidates in the part is marked by the yellow circle. XMM LP-total catalogue. Table 17 lists the XMM-Newton,ROSAT,andChandra fluxes of all SNRs and SNR candidates from the XMM LP-total catalogue that have counterparts classified as SNRs in ROSAT or the XMM-Newton error circle over-plotted on LGGS images. Chandra source lists. In addition, the maximum flux variability From the XMM-Newton source position it looks more likely that and the maximum significance of the variability (following the the X-rays are emitted from the HII region rather than from variability calculation of Sect. 3.6) are given. Three SNRs that the SNR candidate visible in the optical and radio wavelengths. have ROSAT counterparts show variability changing in flux by Nevertheless the XMM-Newton source detected is point-like and more than a factor of five. The most variable source (No. 1066) its hardness ratios lie in the range expected for SNRs. If the ii is discussed below, the second source was discussed in Sect. 10.2 X-ray emission originated from the H -region, it should have (XMMM31 J004434.8+412512, No. 1481), and the third source been detected as spatially extended emission. Thus, No. 1481 (No. 1234) is embedded in the diffuse emission of the central is classified as SNR candidate. A puzzling fact, however, is the area of M 31. In this environment the larger PSF of ROSAT re- pronounced variability between ROSAT and XMM-Newton ob- = . ≈ sults in an overestimate of the source flux, since the contribution servations of Fvar 9 82 with a significance of S var 4(see of the diffuse emission could not be totally separated from the Table 17), which is not consistent with the long term behaviour emission of the point source. of SNRs. There is still the possibility that the detected X-ray ii The remaining four ROSAT sources classified as SNRs and emission does not belong to either the H -region or a SNR at their XMM-Newton counterparts are discussed in the following all. paragraph. SHP97 report that [SHP97] 203 and [SHP97] 211 XMMM31 J004239.8+404318 (No. 969) was already observed (ˆ=[SHL2001] 206) correlate with the same SNR with ROSAT (SHP97, SHL2001) and Chandra (Williams et al. ([DDB80] 1.13), have the same spectral properties and have 2004, s1-84). No optical counterpart is visible on the LGGS luminosities within the range of SNRs. A correlation with the images. The X-ray spectrum, which is shown in Fig. 23,is ROSAT HRI catalogue (PFJ93) reveals that the true X-ray well fitted by an absorbed non-equilibrium ionisation model counterpart of [DDB80] 1.13 is located between the two = ROSAT PSPC sources. Furthermore, PFJ93 report that this with the following best fit values: an absorption of NH . +0.46 × 21 −2 = +32 SNR is located “within 19 of a brighter X-ray source”which 1 76−0.60 10 cm , a temperature of kBT 219−19 eV, and τ = . +0.82 × 8 −3 matches positionally with [SHP97] 211. These findings are an ionisation timescale of 1 75−1.75 10 scm .The 37 −1 confirmed by XMM-Newton and Chandra observations. The unabsorbed 0.2–5 keV luminosity is LX ∼ 6.5 × 10 erg s . ∼ X-ray counterpart of [DDB80] 1.13 is source No. 1066 in The soft spectrum with the temperature of 200 eV is in the XMM LP-total catalogue (or [PFH2005] 354 or r3-69 in good agreement with spectra of old SNRs e.g. in the SMC Kong et al. 2002b). The second source, which correlates with (Filipovic´ et al. 2008). Although the unabsorbed luminosity is [SHP97] 211, is the XMM-Newton source No. 1077, which has rather high for an old SNR, it is still in the range found for a “hard” spectrum and is ∼6.7 times brighter than No. 1066. other SNRs (cf. Kong et al. 2002a; Gaetz et al. 2007). Hence, + Hence, [SHP97] 211 is a blend of the two XMM-Newton sources XMMM31 J004239.9 404318 is classified as a SNR candidate. No. 1066 and No. 1077. This also explains the pronounced variability between [SHL2001] 206 and No. 1066 given in 10.2.1. Comparing SNRs and candidates in XMM-Newton, Table 17. Comparing the Chandra detections of the SNR Chandra and ROSAT catalogues counterpart with the XMM-Newton flux gives a variability factor of Fvar ≈ 1.12. The second ROSAT PSPC catalogue (SHL2001) contains 16 The distance between [SPH97] 203 and [DDB80] 1.13 is sources classified as SNRs. The counterparts of 12 of these ∼>20. [SPH97] 203 was reported only in the first ROSAT

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Table 17. Flux comparison of SNRs and SNR candidates from the XMM LP-total catalogue with counterparts classiﬁed as SNRs in ROSAT and Chandra catalogues.

No. XLPt SHP97 SHL2001 KGP2002+ WGK2004+ Fvar Svar Reason why indicated vaiability is not reliable XID Flux with error in 10−15 erg cm−2 s−1

474 5.27 ± 0.56 21.18 ± 4.46 4.01 3.54 668 7.94 ± 1.36 26.30 ± 6.69 3.31 2.69 883 2.83 ± 0.33 3.33 ± 0.83 1.18 0.56 1040 7.12 ± 0.47 12.49 ± 1.67 1.75 3.11 1050 8.25 ± 0.70 2.50 ± 0.83 3.30 5.28 1066 28.35 ± 1.16 256.16 ± 16.19 39.13 ± 3.33 25.29 ± 5.32 10.13 14.06 ROSAT source is a blend of two XMM-Newton sources 1234 59.12 ± 1.10 152.91 ±13.82 268.98 ±17.09 54.11 ± 3.33 109.13 ± 11.31 4.97 12.34 embedded in diﬀuse emission in central area of M 31 1275 23.88 ± 1.08 53.50 ± 8.47 79.39 ± 9.90 3.32 5.58 1328 9.25 ± 0.74 26.99 1.00 0.00 1351 4.96 ± 0.68 24.96 ± 8.92 17.77 1.00 0.00 1372 2.12 ± 0.84 29.91 1.00 0.00 1410 7.40 ± 0.94 29.87 ± 7.13 4.04 3.12 1481 3.43 ± 0.97 33.66 ± 7.36 9.82 4.07 see Sect. 10.2 1535 14.73 ± 1.31 53.94 ± 9.14 34.41 ± 7.20 3.66 4.25 1599 16.08 ± 0.92 54.39 ±10.03 33.51 ± 6.97 3.38 3.80 1637 12.72 ± 1.33 27.21 1.00 0.00

Notes. (+) KGP2002: Kong et al. (2002b), WGK2004: Williams et al. (2004). ROSAT and Chandra count rates are converted to 0.2–4.5 keV 20 −2 ﬂuxes, using WebPIMMS and assuming a foreground absorption of NH = 6.6 × 10 cm and a photon index of Γ=1.7: ECFSHP97 = −14 −2 −1 −14 −2 −1 −14 −2 −1 2.229×10 erg cm cts ,ECFSHL2001 = 2.249 × 10 erg cm cts ,andECFKGP2002 = 8.325 × 10 erg cm cts . For WGK2004 the lu- −2 −1 −15 36 −1 minosity given in Table 2 of WGK2004 was converted to XID ﬂux using FXID[erg cm s ] = 6.654 × 10 × LWGK2004[10 erg s ].

PSPC catalogue. It was not detected in the observations of the be resolved by XMM-Newton in this environment. The larger second ROSAT PSPC catalogue or in any XMM-Newton or PSF of XMM-Newton is also the reason why source No. 1050 Chandra observation of that region. Thus it seems very likely has a significant variability in Table 17, since this source is lo- that [SPH97] 203 was either a transient source or a false detec- cated within the central diffuse emission of M 31. tion. In both cases [SPH97] 203 cannot be a SNR. As the field Finally, we wanted to determine whether any of the of [DDB80] 1.13 was observed many times with Chandra,and XMM LP-total SNRs and SNR candidates were previously ob- as Chandra has detected weak SNRs in the central part of M 31 served, but not classified as SNRs. In total there are seven such (Kong et al. 2003, and e.g. [DDB80] 1.13), Chandra should have sources. detected X-ray emission corresponding to the ROSAT source One of them (No. 1741) is classified as a SNR candi- [SPH97] 203, if it really belonged to a SNR. date based on its XMM-Newton hardness ratios, and corre- The remaining two ROSAT SNRs correlate with XMM- lates with the Chandra source n1-48 (DKG2004). The fluxes Newton sources, which were not classified as SNRs or SNR can- obtained with XMM-Newton and Chandra are in good agree- didates. Source [SHP97] 258 correlates with source No. 1337 ment (see Table 18), but below the ROSAT detection threshold and has a 3σ positional error of 30. From the improved spatial (5.3 × 10−15 erg cm−2 s−1). resolution of XMM-Newton the total positional error reduces to For a further four sources, the corresponding sources 2 . 3. Hence, we can see that the X-ray source belongs to a fore- were only detected previously with ROSAT. One of them ground star candidate (cf. Table 5) and not to the very nearby (No. 1793= ˆ [SHP97] 347) also correlates with a radio source SNR. Source [SHL2001] 129 correlates with sources No. 743 (source 472 of Braun 1990) and is therefore identified as a SNR. and No. 761, which are classified as a GlC and a GlC candi- The rather high flux variability between the ROSAT and XMM- date, respectively. The SNR candidate listed as the counterpart Newton observations (see Table 18) can be attributed to source of [SHL2001] 129 is located between these two XMM-Newton No. 1799, which is located within 19. 9 of No. 1793. This sug- sources. In addition PFH2005 gives a third source which lies gests that [SHP97] 347 is a combination of both XMM-Newton within the error circle of [SHL2001] 129 and which is classified sources, but as [SHP97] 347 was not detected in SHL2001, we as an AGN candidate. Thus it is very likely that [SHL2001] 129 cannot exclude a transient source or false detection as an expla- is a blend of these three XMM-Newton sources and that the cor- nation for the ROSAT source. Source No. 472 (= ˆ [SHL2001] 84), relation with the SNR candidate has to be considered as a chance source No. 294 (= ˆ [SHP97] 53= ˆ [SHL2001] 56), and source coincidence. No. 1079 (= ˆ [SHP97] 212) are SNR candidates based on their From the sources listed as SNRs in the different Chandra hardness ratios. The pronounced flux variability of source studies many are re-detected. Nevertheless two SNRs from No. 472 is due to source No. 468, which is located within 18. 5 Chandra were not detected in the XMM-Newton observations. of No. 472 and is ∼8.6 times brighter than No. 472. The ob- Source n1-85 has been reported as spatially correlated with an served flux for source No. 1079 was below the ROSAT thresh- optical SNR by Williams et al. (2004), but has also been classi- old. Furthermore, the ROSAT source [SHP97] 212 was classified fied as a repeating transient source in the same paper. An XMM- as a SNR, but did not appear in the SHL2001 catalogue. Hence Newton counterpart to n1-85 was detected neither in the study of ROSAT may have detected an unrelated transient instead. PFH2005 nor in the XMM LP-total catalogue. The transient na- Sources corresponding to the remaining two XMM-Newton ture of this source is at odds with the SNR classification. Source sources were detected with ROSAT and Chandra. Source CXOM31 J004247.8+411556 (Kong et al. 2003), which corre- No. 969 was detected in both ROSAT PSPC surveys lates with the radio source [B90] 95, is located in the vicinity ([SHP97] 185= ˆ [SHL2001] 186) and correlates with Chandra of two bright sources and close to the centre of M 31. Due to source s1-84 (Williams et al. 2006b). We classify it as a XMM-Newton’s larger point spread function this source cannot SNR candidate due to its hardness ratios and X-ray spectrum

A55, page 29 of 51 A&A 534, A55 (2011)

Table 18. Flux comparison of SNRs and SNR candidates from the XMM LP-total catalogue which have counterparts in ROSAT, and/or Chandra catalogues that are not classiﬁed as SNRs.

No. XLPt Chandra PFJ93 SHP97 SHL2001 Fvar Svar Remark‡ XID Flux with error in 10−15 erg cm−2 s−1 (1) (2) (3) (4) (5) (6) (7) (8) (9) 294 18.50 ± 0.85 53.27 ± 6.69 46.78 ± 7.87 2.88 5.16 472 3.15 ± 0.69 26.09 ± 6.07 8.28 3.76 468 brt 969 53.51 ± 1.35 84.51 ± 15.97+ 34.55 ± 6.91 89.06 ± 11.92 2.58 3.96 1079 4.19 ± 0.59 20.06 ± 6.24 4.79 2.53 brt 1291 14.55 ± 0.75 16.04∗ >24.0 35.22 ± 8.47 40.93 ± 7.87 2.81 3.33 1741 4.12 ± 0.65 4.17† 1.01 – brt 1793 3.70 ± 0.52 26.08 ± 6.46 7.06 3.46 1799 brt

Notes. (‡) Source number (from XMM LP-total catalogue) of another (brighter) XMM LP-total source which correlate with the same ROSAT source as the XMM LP-total source given in Col. 1; brt: XMM LP-total flux is below the ROSAT detection threshold (5.3 × 10−15 erg cm−2 s−1). ROSAT 20 −2 and Chandra count rates are converted to 0.2–4.5 keV fluxes, using WebPIMMS and assuming a foreground absorption of NH = 6.6 × 10 cm −14 −2 −1 −14 −2 −1 and a photon index of Γ=1.7: ECFSHP97 = 2.229 × 10 erg cm cts ,ECFSHL2001 = 2.249 × 10 erg cm cts ,ECFHRI = 6.001 × −14 −2 −1 † −12 −2 −1 (+) 10 erg cm cts , :ECFDKG2004 = 5.56×10 erg cm cts . For WGK2004 the luminosity given in Table 2 of WGK2004 was converted −2 −1 −15 36 −1 (∗) to XID flux using FXID[erg cm s ] = 6.654 × 10 × LWGK2004[10 erg s ]. For VG2007 the luminosity given in Table 2 of VG2007 was −2 −1 −15 36 −1 converted to XID flux using FXID[erg cm s ] = 9.433 × 10 × LVG2007[10 erg s ].

(see XMMM31 J004239.8+404318). Counterparts for source No. 1291 were reported in the literature as [PFJ93] 84, [SHP97] 251, [SHL2001] 255, [VG2007] 261 and source 4 in Table 5 of Orio (2006). Based on the XMM-Newton hardness ) ratios and the correlation with radio source [B90] 166 (Braun −2 1990), we identified the source as a SNR. For sources No. 294, No. 969, and No. 1291 the variability between different observations may not be real because of systematic cross-calibration uncertainties. Therefore, we keep the SNR and SNR classifications for these sources.

10.2.2. The spatial distribution Number of sources per area (deg To examine the spatial distribution of the XMM-Newton SNRs and SNR candidates, we determined de-projected distances from 0510 0 5 10 15 20 25 30 the centre of M 31. The distribution of SNRs and SNR candi- Distance (kpc) dates (normalised per deg2) is shown in Fig. 24. It shows an enhancement of sources around ∼3 kpc, which corresponds to the Fig. 24. De-projected radial distribution of SNRs and SNR candidates SNR population in the “inner spiral arms” of M 31. In addition, a from the XMM LP-total catalogue. An enhancement in the source dis- second enhancement of sources around ∼10 kpc is detected; this tribution corresponding to the 10 kpc dust ring of M 31 is visible. The distribution of identified SNRs is shown in blue. corresponds to the well known dust ring or star formation ring in the disc of M 31 (Block et al. 2006). Only a few sources are located beyond this ring. Figure 25 shows the spatial distribu- of gravitational energy from the accreted matter into radiation tion of the SNRs and SNR candidates from the XMM LP-total by a mass-exchange from the companion star onto the compact catalogue plotted over the IRAS 60 μmimage(Wheelock et al. object. 1994). We see that most of the SNRs and SNR candidates are lo- X-ray binaries containing an NS or a BH are divided into two cated on features that are visible in the IRAS image. This again main classes, depending on the mass of the companion star: demonstrates that SNRs and SNR candidates are coincident with the dust ring at ∼10 kpc. In addition, the locations of star forming – low mass X-ray binaries (LMXBs) contain companion stars of low mass (M ∼< 1 M ) and late type (type A or later), regions obtained from GALEX data (Kang et al. 2009, and priv. ∼ 8−9 comm.) are indicated in Fig. 25. We see that many of the SNRs and have a typical lifetime of 10 yr (Fabbiano 2006). and SNR candidates are located within or next to star forming LMXBs can be located in globular clusters. Mass transfer regions in M 31. from the companion star into an accretion disc around the compact object occurs via Roche-lobe overflow; – high mass X-ray binaries (HMXBs) contain a massive > 10.3. X-ray binaries O or B star companion (Mstar ∼ 10 M , Verbunt & van den Heuvel 1995) and are short-lived with lifetimes of X-ray binaries consist of a compact object plus a companion ∼106−7 yr (Fabbiano 2006). One has to distinguish between star. The compact object can either be a white dwarf (these sys- two main groups of HMXBs: super-giant and the Be/X-ray tems are a subclass of CVs), a neutron star (NS), or a black binaries. In these systems wind-driven accretion onto the hole (BH). A common feature of all these systems is that a large compact object powers the X-ray emission. Mass-accretion amount of the emitted X-rays is produced due to the conversion via Roche-lobe overflow is less frequent in HMXBs, but is

A55, page 30 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Fig. 26. Distribution of the source fluxes of XRBs and GlC sources in the 0.2–4.5 keV (XID) band. The diagram shows the number of identified and classified XRBs and GlCs at each flux bin, plotted versus the flux. In addition, the individual distribution of (field) XRBs (in red) as well as GlCs (in green) are given. Fig. 25. An IRAS 60 μmimage(Wheelock et al. 1994), which clearly shows the dust ring located at ∼10 kpc, over-plotted with the location of SNRs (red dots) and candidates (green dots) from the XMM LP-total reported as X-ray binaries in the literature (see comment col- catalogue. The coincidence between the SNRs and candidates and the umn of Table 5). Figure 26 (red histogram) shows the flux structures of the image is visible. In addition the locations of star form- distribution of XRBs. We see that this class contains only ing regions, which were obtained from GALEX data (Kang et al. 2009), are indicated by blue dots. Furthermore the two ellipses (green) at 3 and rather bright sources. This is not surprising as the classifica- 10 kpc from the centre correspond to the enhancemnets of sources from tion criterion for XRBs is based on their variability, which Fig. 24. is more easily detected for brighter sources (cf. Sect. 6). The XID fluxes range from 1.4 × 10−14 erg cm−2 s−1 (No. 378) to 3.75 × 10−12 erg cm−2 s−1 (No. 966), which correspond to lumi- still known to occur in several bright systems (e.g. LMC X-4, nosities from 1.0 × 1036 erg s−1 to 2.7 × 1038 erg s−1. SMC X-1, Cen X-3). HMXBs are expected to be located in It is clear from Fig. 27, which shows the spatial distribution areas of relatively recent star formation, between 25–60 Myr of the XRBs, that nearly all sources classified or identified as ago (Antoniou et al. 2010). XRBs (yellow dots) are located in fields that were observed more than once (centre and southern part of the disc). This is partly a We should expect about 45 LMXBs in M 31, following a simi- selection effect, caused by the fact that these particular fields lar estimation as the one presented in Sect. 10.2. Here the num- were observed several times, thus allowing the determination of ber of LMXBs in the Galaxy was estimated from Grimm et al. source variability. For sources located outside these fields, es- (2002). In the XMM LP-total catalogue 88 sources are identi- pecially the northern part of the disc, the transient nature must fied/classified as XRBs. This is not surprising as we may expect have been reported in the literature to mark them as an XRBs. M 31 to have a higher fraction of XRBs than the Galaxy since The source density of LMXBs, which follows the overall stel- it is an earlier type galaxy composed of a higher fraction of old lar density, is higher in the centre than in the disc of M 31. One stars. would not expect HMXBs in the central region which is domi- XRBs are the main contribution to the population of “hard” nated by the bulge (old stellar population). From Fig. 28,which X-ray sources in M 31. Despite some more or less reliable can- shows the spatial distribution of the XRBs over-plotted on an didates, not a single, definitely detected HMXB is known in IRAS 60 μmimage(Wheelock et al. 1994), we see that only a M 31. The results of a new search for HMXB candidates are few sources, classified or identified as XRBs, are located in the presented in Sect. 10.3.2. The LMXBs can be separated into two vicinity of star forming regions. sub-classes: the field LMXBs (discussed in this section) and References for the sources, selected from their temporal vari- those located in globular clusters. Sources belonging to the latter ability, are given in Table 9. TPC06 report on four bright X- sub-class are discussed in Sect. 10.4. ray transients, which they detected in the observations of July The sources presented here are classified as XRBs, because 2004 and suggested to be XRB candidates. We also found these they have HRs indicating a hard source and are either transient sources and classified source No. 705 and identified sources or show a variability factor greater than ten (see Sect. 6). No. 985, No. 1153, No. 1177 as XRBs. One of the identified In total ten sources are identified and 26 are classi- XRBs (No. 1177) shows a very soft spectrum. Williams et al. fied as XRBs by us, according to the classification criteria (2005b) observed source No. 1153 with Chandra and HST.From given in Table 6. Apart from source No. 57 (XMMM31 the location and X-ray spectrum they suggest it to be an LMXB. J003833.2+402133, see below), the identified XRBs had been They propose that the optical counterpart of the X-ray source is

A55, page 31 of 51 A&A 534, A55 (2011)

15 arcmin

15 arcmin

Fig. 27. The spatial distribution of XRBs and candidates from the Fig. 28. The spatial distribution of XRBs and candidates from the XMM LP-total catalogue. The positions of the XRBs and candidates XMM LP-total catalogue. Shown are the same sources as in Fig. 27,but are marked with yellow dots; the two XRB candidates classified from over-plottedonanIRAS60μmimage(Wheelock et al. 1994), which their variability compared with ROSAT observations are marked with shows the dusty star forming region in M 31. In addition the locations blue dots. An increase in the number density of sources in the central of star forming regions, which were obtained from GALEX data (Kang field is clearly visible. In addition the two new HMXB candidates pre- et al. 2009), are indicated by cyan dots. sented in Sect. 10.3.2 (red dots), and the three HMXB candidates of SBK2009 that satisfy our U − B/B − V selectrion criterion (green dots, see Sect. 10.3.2) are shown. XRBs which correlate with globular clusters are shown in Fig. 31. blackbody luminosity to the total luminosity is ∼59%. Formally acceptable fits are also obtained from an absorbed disc blackbody and an absorbed bremsstrahlung model (see Table 19). a star within the X-ray error box , which shows an optical bright- We did not find any significant feature in a fast Fourier trans- ness change (in B) by 1 mag. Source No. 985 was first detected formation (FFT) periodicity search. The combined EPIC light in January 1979 by TF91 with the Einstein observatory. WGM06 curve during observation s32 was consistent with a constant rediscovered it in Chandra observations from 2004. Their coor- value. dinated HST ACS imaging does not reveal any variable optical To identify possible optical counterparts we examined the counterpart. From the X-ray spectrum and the lack of a bright LGGS images and the images taken with the XMM-Newton op- star, WGM06 suggest that this source is an LMXB with a black tical monitor during the X-ray observation (UVW1 and UVW2 hole primary. filters). The absence of optical/UV counterparts and of variabil- In the following subsections we discuss three transient XRBs ity on short timescales, as well as the spectral properties suggest in more detail. that this source is a black hole LMXB in the steep power-law state (McClintock & Remillard 2006). XMMM31 J003833.2+402133 (No. 57) was first detected in the XMM-Newton observation from 02 January 2008 (s32) at an CXOM31 J004059.2+411551: Galache et al. (2007) reported unabsorbed 0.2–10 keV luminosity of ∼2 × 1038 erg s−1.From on the detection of a previously unseen X-ray source in a 5 ks two observations, taken about 0.5 yr (s31) and 1.5 yr (s3) earlier, Chandra ACIS-S observation from 05 July 2007. In an XMM- we derived upper limits for the fluxes, which were more than a Newton ToO observation (sn11, Stiele et al. 2007) taken about factor of 100 below the values obtained in January 2008. 20 days after the Chandra detection, the source (No. 523) was The combined EPIC spectrum from observation s32 still bright. The position agrees with that found by Chandra.We (Fig. 29a) is best fitted with an absorbed disc blackbody plus detected the source at an unabsorbed 0.2–10 keV luminosity of = . +0.42 × 21 −2 ∼1.1 × 1038 erg s−1. power-law model, with NH 1 68−0.48 10 cm ,temperature at the inner edge of the disc kBTin = 0.462 ± 0.013 keV The combined EPIC spectrum (Fig. 29b) can be well . +0.33 and power-law index of 2 55−1.05. The contribution of the disc fitted with an absorbed disc blackbody model with A55, page 32 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

XMMM31 J003833.2+402133 XMM−Newton, EPIC during the X-ray observation did not reveal any possible optical/UV counterparts. pn FF thin mos1 FF medium mos2 FF medium The lack of bright optical counterparts and the X-ray param-

−1 eters (X-ray spectrum, lack of periodicity, transient nature, lumi- keV

−1 nosity) are consistent with this source being a black hole X-ray

0.01 0.1 transient, as already mentioned in Galache et al. (2007). Counts s −3 10 XMMU J004144.7+411110 (No. 705) was detected by Trudolyubov et al. (2006)inXMM-Newton observations b1–b4 (July 2004) at an unabsorbed luminosity of 37 −1 Residials 3.1–4.4 × 10 erg s in the 0.3–7 keV band, using a

−0.05 0 0.05 0.5110 2 5 DISKBB model. We detected the source in observation sn11 Channel Energy (keV) (25 July 2007) with an unabsorbed 0.2–10 keV luminosity of − (a) XMMM31 J003833.2+402133 ∼1.8 × 1037 erg s 1, using also a DISKBB model. In observation sn11, the source was bright enough to al- CXOM31 J004059.2+411551 XMM−Newton, EPIC low spectral analysis. The spectra can be well ﬁtted with an absorbed power-law, disc blackbody or bremsstrahlung model pn FF thin mos1 FF medium (Table 19). The obtained spectral shapes (absorption and temper- mos2 FF medium

−1 ature as well as photon index) are in agreement with the values

keV of Trudolyubov et al. (2006). −1 An FFT periodicity search did not reveal any signiﬁcant pe- Counts s

0.01 0.1 riodicities in the 0.3 s to 2000 s range. No optical counterparts were evident in the images taken with the XMM-Newton optical monitor UVW1 and UVW2 during the sn11 observation, nor in the LGGS images. The lack of a bright optical counterpart and the X-ray parameters support Residials that this source is a black hole X-ray transient, as classiﬁed by

−0.05 0 0.05 0.1 0.51 2 Channel Energy (keV) Trudolyubov et al. (2006). (b) CXOM31 J004059.2+411551 10.3.1. Sources from the XMM-LP total catalogue that were XMMU J004144.7+411110 XMM−Newton, EPIC not detected by ROSAT

pn FF thin To search for additional XRB candidates, we selected all sources mos1 FF medium mos2 FF medium from the XMM LP-total catalogue, that were classiﬁed as hard 0.01 −1 and which did not correlate with a source listed in the ROSAT keV

−1 catalogues (PFJ93, SHP97 and SHL2001). The ﬂux distribution

−3 of the selected sources is shown in Fig. 30, and Table 20 gives 10 Counts s the number of sources brighter than the indicated ﬂux limit. Possible, new XRB candidates are sources that have an XID ﬂux that lies at least a factor of ten above the ROSAT detection threshold (5.3 × 10−15 erg cm−2 s−1). These

0 0.01 sources fulfil the variability criterion used to classify XRBs Residials (cf. Sect. 6). The XMM LP-total catalogue lists five sources 0.51 2 5 Channel Energy (keV) without ROSAT counterparts that have XID fluxes above 5.3 × 10−14 erg cm−2 s−1. These are: No. 239, No. 365, No. 910, (c) XMMU J004144.7+411110 No. 1164, and No. 1553. Between the ROSAT and XMM-Newton observations more than ten years have elapsed. On this time Fig. 29. EPIC spectra of the transient sources a) scale AGN can also show strong variability. To estimate the XMMM31 J003833.2+402133, b) CXOM31 J004059.2+411551 and c) XMMU J004144.7+411110. The histograms show the best-fit number of AGN among the five sources listed above, we in- model: PL+DISCBB in a), DISCBB in b) and c). vestigated how many sources of the identified and classified background objects from the XMM LP-total catalogue with an XID flux higher than 5.3 × 10−14 erg cm−2 s−1 were not detected by ROSAT. The result is that ROSAT detected all background = . ± . × 21 −2 − − − NH (2 00 0 16) 10 cm and with a temperature at sources with an XID flux higher than 5.3 × 10 14 erg cm 2 s 1 = . ± . the inner edge of the disc of kBTin 0 538 0 017 keV that are listed in the XMM LP-total catalogue. Thus, the prob- (Table 19). The spectral parameters and luminosity did not ability that any of the five sources listed above is a background change significantly compared to the Chandra values of object is very low, in particular if the source is located within Galache et al. (2007). the D25 ellipse of M 31. Therefore, the two sources located We did not find any significant feature in an FFT periodicity within the D25 ellipse are listed in the XMM LP-total catalogue search. The combined EPIC light curve was consistent with a as XRB candidates, while the remaining three sources, which constant value. are located outside the D25 ellipse, are classified as hard .All The examination of LGGS images and of images taken with five sources are marked in the comment column of Table 5 with the XMM-Newton optical monitor (UVW1 and UVW2 filters) “XRB cand. from ROSAT corr.”.

A55, page 33 of 51 A&A 534, A55 (2011)

Table 19. Spectral parameters of the transient sources. √ ∗ χ2 † M 31 ﬁeld Model NH kBTRin cos i Photon LX Instrument ( × 1021 cm−2) (keV) (km) Index (d.o.f.)

XMMM31 J003833.2+402133 (No. 57) + . +0.42 . ± . +9 . +0.33 + + s32 PL DISCBB 1 68−0.48 0 462 0 013 106−10 2 55−1.05 173.89(145) 2.04 PN M1 M2 s32 DISCBB 1.06 ± 0.06 0.511 ± 0.009 95 ± 4 270.01(147) 1.46 PN+M1+M2 . ± . . +0.029 + + s32 BREMSS 1 91 0 07 1 082−0.030 208.65(147) 2.12 PN M1 M2 CXOM31 J004059.2+411551 (No. 523) sn11 DISCBB 2.00 ± 0.16 0.538 ± 0.017 75 ± 6 97.70(79) 1.12 PN+M1+M2 . ± . . +0.060 + + sn11 BREMSS 3 13 0 19 1 097−0.056 93.17(79) 1.72 PN M1 M2 XMMU J004144.7+411110 (No. 705) . +1.03 . +0.100 +13 + + sn11 DISCBB 2 32−0.87 0 586−0.087 26−8 29.74(23) 0.18 PN M1 M2 . +1.14 . +0.373 + + sn11 BREMSS 3 72−1.00 1 216−0.269 29.48(23) 0.29 PN M1 M2 . +1.72 . +0.46 + + sn11 PL 6 17−1.47 3 23−0.40 31.57(23) 1.12 PN M1 M2

Notes. (∗) Eﬀective inner disc radius, where i is the inclination angle of the disc; (†) unabsorbed luminosity in the 0.2–10.0 keV energy range in units of 1038 erg s−1.

lead at best to an overlap – in the worst case to a fusion – with the area occupied by other hard sources (Colbert et al. 2004). Based on the spectral analysis of individual sources of M 31, SBK2009 identified 18 HMXB candidates with power- law indices between 0.8 and 1.2. One of these sources ([SBK2009] 123) correlates with a globular cluster, and hence it is rather an LMXB in a very hard state rather than an HMXB (cf. Trudolyubov & Priedhorsky 2004). Four of their sources ([SBK2009] 34, 106, 149, and 295) do not have counterparts in the XMM LP-total catalogue. Eger (2008) developed a selection algorithm for HMXBs in the SMC, which also uses properties of the optical companion. X-ray sources were selected as HMXB candidates if they had HR2 + EHR2 > 0.1 as well as an optical counterpart within 2. 5 of the X-ray source, with −0.5 < B − V < 0.5mag, −1.5 < U − B < −0.2 mag and V < 17 mag. We tried to transfer this SMC selection algorithm to M 31 sources. In doing so, we encountered two problems: the first problem is that the region of the U − B/B − V diagram is also populated by globular clusters (LMXB candidates) in M 31. The second problem is that due to the much greater distance to M 31, Fig. 30. Distribution of the source fluxes in the 0.2–4.5 keV (XID) band. the range of detected V magnitudes of HMXBs in the SMC of The diagram shows the number of sources from the XMM LP-total cat- ∼13 < V < 17 mag translates to a ∼19 < V < 23 mag criterion alogue that were classified as hard , and in addition do not correlate with a source listed in the ROSAT catalogues at each flux bin plotted for M 31. Thus the V mag of optical counterparts of possible versus the flux, using logarithmic scales. HMXB candidates lies in the same range as the optical counterparts of AGN. Therefore the V mag criterion, which provided most of the discriminatory power in the case of the SMC, fails totally in the case of M 31. 10.3.2. Detection of high mass X-ray binaries A few of the sources selected from the optical colour-colour As already mentioned, until now not a single secure HMXB in diagram and HR diagrams are bright enough to allow the cre- M 31 has been confirmed. The reason for this is that the de- ation of X-ray spectra. That way two additional (i.e. not given in tection of HMXBs in M 31 is difficult. Colbert et al. (2004) SBK2009) HMXB candidates were found. showed that the hardness ratio method is very inefficient in se- In addition, we determined the reddening free Q parameter: lecting HMXBs in spiral galaxies. The selection process is complicated by the fact, that the spectral properties of BH HMXBs, Q = (U − B) − 0.72(B − V)(8) which have power-law spectra with indices of ∼1–∼2aresim- ilar to LMXBs and AGN. Therefore the region in the HR dia- (for definition see e.g. Cox 2001) which allowed us to keep only grams where BH HMXB are located is contaminated by other the intrinsically bluest stars, using Q ≤−0.4 (O-type stars typ- hard sources (LMXBs, AGN, and Crab-like SNRs). For the ically have Q < −0.9, while –0.4 corresponds to a B5 dwarf or NS HMXBs, which have power-law indices of ∼1, and thus giant or an A0 supergiant, Massey et al. 2007). U − B and B − V should be easier to select, the uncertainties in the hardness ratios were taken from the LGGS catalogue.

A55, page 34 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 20. Cumulative number of sources classiﬁed as hard in the XMM LP-total catalogue and without ROSAT counterpart.

XID ﬂux limit # of sources erg cm−2 s−1 5.5 E-15 539 1 E-14 242 5E-14 7 1E-13 1

Notes. Given is the cumulative number of sources brighter than the indicated ﬂux limit.

Table 21. Reddening free Q parameter for HMXB candidates of SBK2009.

No. [SBK2009] LGGS counterpart Q 312 21 J004001.50+403248.0 –0.34 1668 236 J004538.23+421236.0 –0.77 1724 256 J004558.98+420426.5 –0.81 1109 123 J004301.51+413017.5 +1.77 1436 172 J004420.98+413546.7 –0.65 J004421.01+413544.3∗ -0.29 1630 226 J004526.68+415631.5 –0.92 J004526.58+415633.1∗ –0.72

(∗) Notes. Counterparts listed in SBK2009. 15 arcmin

XMMM31 J004557.0+414830 (No. 1716) has an USNO-B1 (R2 = 18.72 mag), a 2MASS and an LGGS (V = 20.02 mag; = − . χ2 = Fig. 31. The spatial distribution of X-ray sources correlating with GlCs Q 0 44) counterpart. The EPIC spectrum is best ﬁtted ( red . = . +6.0 × 21 −2 and candidates from the XMM LP-total catalogue (yellow dots). An 0 93) by an absorbed power-law with NH 7 4−3.9 10 cm enhancement of sources towards the central region of M 31 is clearly and photon index Γ=1.2 ± 0.4. The absorption corrected X-ray visible. luminosity in the 0.2–10 keV band is ∼7.1 × 1036 erg s−1.

XMMM31 J004506.4+420615 (No. 1579) has an USNO-B1 sources corresponding to globular clusters are identified by (B2 = 20.87 mag), a 2MASS and an LGGS (V = 20.77 mag; Q = cross-correlating with globular cluster catalogues (see Sect. 3.8). −1.04) counterpart. The EPIC PN spectrum is best fitted (χ2 = Therefore changes between the XMM LP-total catalogue and the red catalogue of PFH2005 in the classification of sources related to 1.6) by an absorbed power-law with N = 0.48+2.4 × 1021 cm−2 H −1.0 globular clusters are based on the availability of and modifica- Γ= . +0.7 and photon index 1 0−0.5. The absorption corrected X-ray tions in recent globular cluster catalogues. − luminosity in the 0.2–10 keV band is ∼8.6 × 1036 erg s 1. In total 52 sources of the XMM LP-total catalogue correlate To strengthen these classifications spectroscopic optical with (possible) globular clusters. Of these sources 36 are identi- follow-up observations of the optical counterparts are needed. fied as GlCs because their optical counterparts are listed as glob- An FFT periodicity search did not reveal any significant period- ular clusters in the catalogues given in Sect. 3.8, while the re- icities for either of the two sources and the light curves do not maining 16 sources are only listed as globular cluster candidates. show eclipses. The range of source XID fluxes goes from From the sources reported as HMXB candidates in 3.1 × 10−15 erg cm−2 s−1 (No. 924) to 2.7 × 10−12 erg cm−2 s−1 SBK2009, three sources ([SBK2009] 21, 236, and 256) are lo- (No. 1057), or in luminosity from 2.3 × 1035 erg s−1 to cated in the region of the U − B/B − V diagram, that we used. 2.0 × 1038 erg s−1 (Fig. 26; green histogram). Compared to the Another three sources ([SBK2009] 123, 172, and 226) are lo- fluxes found for the XRBs discussed in Sect. 10.3, 14 sources cated outside that region. The remaining sources of SBK2009 that correlate with GlCs have fluxes below the lowest flux have either no counterparts with a U − B colour entry in found for field XRBs. The reason for this finding is that the the LGGS catalogue ([SBK2009] 99, 234, 294, and 302) or classification of field XRBs is based on the variable or transient have no optical counterpart from the LGGS catalogue at all nature of the sources, which can only be to detected for brighter ([SBK2009] 9, 160, 197, and 305). The reddening free Q pa- sources (cf. Sect. 6) and not just by positional coincidence that rameter for the SBK2009 sources that have counterparts in the is also possible for faint sources. LGGS catalogue are given in Table 21. Figure 31 shows the spatial distribution of the GlC sources. X-ray sources correlating with GlCs follow the distribution of 10.4. Globular cluster sources the optical GlCs, which are also concentrated towards the central region of M 31. A significant number of the luminous X-ray sources in the The three brightest globular cluster sources, which Galaxy and in M 31 are found in globular clusters. X-ray are located in the northen disc of M 31, are

A55, page 35 of 51 A&A 534, A55 (2011)

Integrated Colour distribution of Globular Clusters Table 22. Integrated V − I colours, dereddened V − I integrated colours, and age estimates of the globular clusters in which the X ray sources are located.

Name Class∗ Age+ V mag VI VI0 Age†

B005 confirmed old 15.69 1.29 1.15 old SK055B candidate – 18.991 0.388 0.248 – B024 confirmed old 16.8 1.15 1.01 old SK100C candidate na 18.218 1.181 1.041 old B045 confirmed old 15.78 1.27 1.13 old B050 confirmed old 16.84 1.18 1.04 old B055 confirmed old 16.67 1.68 1.54 old B058 confirmed old:: 14.97 1.1 0.96 old-inter MITA140 confirmed old 17 9999 – – B078 confirmed old 17.42 1.62 1.48 old B082 confirmed old 15.54 1.91 1.77 old B086 confirmed old 15.18 1.26 1.12 old SK050A confirmed – 18.04 1.079 0.939 old-inter B094 confirmed old 15.55 1.26 1.12 old B096 confirmed old 16.61 1.48 1.34 old B098 confirmed old 16.21 1.13 0.99 old-inter B107 confirmed old 15.94 1.28 1.14 old B110 confirmed old 15.28 1.28 1.14 old B117 confirmed old:: 16.34 1 0.86 inter B116 confirmed old 16.79 1.86 1.72 old B123 confirmed old 17.416 1.29 1.15 old B124 confirmed old 14.777 1.147 1.007 old B128 confirmed old:: 16.88 1.12 0.98 old-inter B135 confirmed old 16.04 1.22 1.08 old Fig. 32. The distribution of (V − I)0 for globular clusters (and candi- B143 confirmed old 16 1.22 1.08 old dates), with the approximate age-ranges marked, hosting XMM LP- B144 confirmed old:: 15.88 0.59 0.45 young total X-ray sources. B091D confirmed old 15.44 9999 – – B146 confirmed old:: 16.95 1.09 0.95 interm B147 confirmed old 15.8 1.27 1.13 old B148 confirmed old 16.05 1.17 1.03 old B150 confirmed old 16.8 1.28 1.14 old No. 1057 (XMMM31 J004252.0+413109), No. 694 B153 confirmed old 16.24 1.3 1.16 old (XMMM31 J004143.1+413420), and No. 1692 B158 confirmed old 14.7 1.15 1.01 old + B159 confirmed old 17.2 1.41 1.27 old (XMMM31 J004545.8 413941). They are all brighter than B161 confirmed old 16.33 1.1 0.96 old-inter 37 −1 8.4 × 10 erg s . Source No. 694 was classified as a black B182 confirmed old 15.43 1.29 1.15 old hole candidate, due to its variability observed at such high B185 confirmed old 15.54 1.18 1.04 old B193 confirmed old 15.33 1.28 1.14 old luminosities. A detailed discussion of the three sources is given SK132C candidate - 18.342 1.84 1.7 old in Barnard et al. (2008). B204 confirmed old 15.75 1.17 1.03 old + B225 confirmed old 14.15 1.39 1.25 old XMMM31 J004303.2 412121 (No. 1118) was identified as B375 confirmed old 17.61:: 1.02 0.88 interm a foreground star in PFH2005, based on the classification in the B386 confirmed old 15.547 1.154 1.014 old

“Revised Bologna Catalogue” (Galleti et al. 2004). Galleti et al. (∗) (2004) took the classification from Dubath & Grillmair (1997), Notes. Classification as confirmed or otherwise comes from the revised Bologna catalogue (December 2009, Version 4) http:// which is based on the velocity dispersion of that source. Recent www.bo.astro.it/M31/RBC_Phot07_V4.tab. (+) age comes from “HST images unambiguously reveal that this [B147] is a well re- Caldwell et al. (2009). V,andV−I are integrated colours that come from solved star cluster, as recently pointed out also by Barmby et al. the revised Bologna catalogue (December 2009, Version 4) http:// (2007)”(Galleti et al. 2007). That is why source No. 1118 is now www.bo.astro.it/M31/RBC_Phot07_V4.tab,(V − I)0 is the dered- identified as an XRB located in globular cluster B147. dened V −I integrated colour, assuming E(B−V) = 0.10±0.03, which is the average of the reddenings of all M 31 clusters in Rich et al. (2005). (this E(B − V) corresponds to E(V − I) = 0.14). (†) This dereddened 10.4.1. Integrated optical properties of the globular clusters colour (V − I)0 is used to estimate the age on the basis of the plots in which the X ray sources are located (V − I)0 versus log Age from Sarajedini et al. (2007). For each X-ray source which correlates with a globular cluster or globular cluster candidate in the optical, we investigated its integrated V − I colour and derived age estimates. Table 22 lists the name of the optical counterpart, its classification according to RBC V.4 (Galleti et al. 2009), the age classification of Caldwell distribution of (V − I) for our clusters, with the approximate − 0 et al. (2009), the V magnitude and V I colour given in RBC V.4, age-ranges marked. the dereddened V − I colour, and the age estimate derived by ourselves. In general there is good agreement between the Caldwell The integrated V − I colours of the clusters can be found in et al. (2009) and our age estimates. This result indicates that the RBC V.4 and can be used to provide estimates of the ages of the great majority of the objects are indeed old globular clusters. clusters, in conjunction with reddening values. We have adopted Figure 33 shows the distribution of (V − I)0 for all confirmed a reddening of E(B−V) = 0.10±0.03, which is the average of the and candidate globular clusters, listed in the RBC V.4, which are reddenings of all M 31 clusters in Rich et al. (2005). Using these located in the XMM LP-total field, and which have V as well values, we have derived (V − I) for our clusters. In most cases as I magnitudes given. A comparison with Fig. 32 again reveals 0 > (V − I)0 > 1.0 suggesting clusters older than 2 Gyr according that mainly counterparts of old globular clusters (age ∼2Gyr) to Sarajedini et al. (2007). The histogram in Fig. 32 shows the are detected in X-rays.

A55, page 36 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Table 23. Variability between XMM LP-total and ROSAT observations for sources classiﬁed as GlC candidates in the ROSAT PSPC surveys.

SRC SI∗ SII∗ XFLUX+ EXFLUX+ fv_SI† sv_SI† fv_SII† sv_SII† type SIf‡ SIIf‡ (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) 383 73 68 1.45E-12 1.05E-14 1.26 11.58 1.23 9.04 GlC * * 403 79 74 2.55E-14 2.36E-15 2.61 2.09 7.57 4.92 Gal 422 76 2.01E-14 1.43E-15 hard 694 122 113 1.52E-12 1.04E-14 1.38 10.56 1.26 7.46 GlC * * 793 138 136 4.76E-14 2.33E-15 1.10 0.55 1.02 0.14 Gal * 841 150 147 1.40E-12 1.61E-14 1.77 19.81 2.11 26.37 GlC * – 855 158 154 4.21E-13 3.70E-15 1.01 0.14 3.54 48.75 GlC * 885 168 163 1.56E-14 1.60E-15 1.70 1.54 GlC 923 175 175 1.47E-13 2.07E-15 1.87 7.68 1.30 3.44 GlC 933 178 3.67E-14 1.64E-15 3.03 7.03 GlC 947 180 179 3.24E-13 7.46E-15 2.43 12.78 2.29 12.16 GlC * – 966 184 184 3.51E-12 9.21E-15 1.00 0.20 2.31 151.58 XRB 1057 205 199 2.67E-12 2.05E-14 1.72 26.26 1.79 28.48 GlC * * 1102 217 211 3.23E-13 2.93E-15 1.06 1.04 5.51 60.80 GlC * 1109 218 212 3.25E-13 9.08E-15 1.91 9.70 2.10 10.72 GlC * * 1118 222 216 1.16E-13 2.03E-15 1.46 3.63 1.89 7.46 GlC 1122 223 217 2.48E-13 2.72E-15 2.08 12.02 7.03 73.27 GlC 1157 228 223 7.59E-13 4.48E-15 1.06 1.68 1.08 2.75 GlC * * 1171 229 227 4.68E-13 4.93E-15 1.82 12.92 1.75 12.19 GlC * * 1262 247 249 2.94E-14 3.10E-15 14.11 18.40 14.64 20.24 1267 247 249 4.80E-13 4.57E-15 1.16 3.04 1.11 2.44 GlC * * 1289 250 254 2.88E-14 1.91E-15 1.16 0.57 1.98 3.15 GlC * 1293 250 254 6.70E-15 9.42E-16 3.73 2.80 8.53 5.72 AGN 1296 253 257 3.89E-14 1.58E-15 4.03 9.38 1.25 1.17 GlC 1297 252 258 5.59E-15 9.61E-16 4.46 2.69 hard 1305 258 1.69E-14 9.87E-16 GlC 1340 261 266 6.07E-14 3.01E-15 1.77 4.20 1.30 1.64 GlC * 1357 258 7.04E-15 1.18E-15 hard 1449 281 289 2.34E-14 1.00E-15 3.10 5.36 1.79 2.39 fg Star 1463 282 290 7.51E-13 8.38E-15 1.13 3.33 1.33 7.64 GlC * * 1634 302 316 7.70E-14 2.91E-15 3.14 5.60 1.89 4.33 hard ** 1692 318 336 1.15E-12 2.00E-14 2.86 45.59 2.62 38.63 GlC * 1803 349 354 8.72E-13 9.17E-15 1.32 7.87 1.03 0.93 GlC * *

Notes. (∗) SI: SHP97, SII: SHL2001 (+) XID Flux and error in erg cm−2 s−1. (†) Variability factor and significance of variability, respectively, for comparisons of XMM-Newton XID fluxes to ROSAT fluxes listed in SPH97 and SHL2001, respectively. (‡) An asterisk indicates that the XID flux is higher than the corresponding ROSAT flux. ROSAT count rates are converted to 0.2–4.5 keV fluxes, using WebPIMMS and assuming 20 −2 −14 −2 −1 a foreground absorption of NH = 6.6 × 10 cm and a photon index of Γ=1.7: ECFSHP97 = 2.229×10 erg cm cts and ECFSHL2001 = 2.249 × 10−14 erg cm−2 cts−1.

10.4.2. Comparing GlC and candidates in XMM-Newton, correlates with sources No. 1289 and No. 1293, where the for- Chandra and ROSAT catalogues mer is the X-ray counterpart of the globular cluster candidate mita 311 (Magnier 1993). [SHL2001] 258 has a 1σ positional The combined ROSAT PSPC catalogue (SHP97 and SHL2001) errorof48 and thus correlates with sources No. 1297, No. 1305 contains 33 sources classified as globular cluster counterparts. and No. 135724. The brightest of these three sources (No. 1305), Of these sources one is located outside the field observed with which is actually located closest to the ROSAT position, corre- XMM-Newton. Another two sources do not have counterparts in lates with the globular cluster candidate SK 132C (RBC V3.5). the XMM LP-total catalogue. The first one is [SHL2001] 232, Table 23 gives the variability factors (Cols. 6, 8) and sig- which is not visible in any XMM-Newton observation taken be- nificance of variability (7, 9) for sources classified as GlC can- fore December 2006 as was already reported in Trudolyubov & didates in the ROSAT PSPC surveys. For most sources only Priedhorsky (2004). The second source ([SHL2001] 231) cor- low variability is detected. The two sources with the high- relates with B 164 which is identified as a globular cluster in est variability factors found (No. 1262, No. 1293) belong to RBC V3.5. In addition [SHL2001] 231 is listed in PFH2005 as ROSAT sources with more than one XMM-Newton counterpart. the counterpart of the source [PFH2005] 423. Due to the im- In these cases the XMM-Newton sources that correlate with the proved positional accuracy of the X-ray source in the XMM- same ROSAT source and the optical globular cluster source Newton observations, PFH2005 rejected the correlation with show much weaker variability. Interestingly, a few sources show B 164 and instead classified [PFH2005] 423 as a foreground star low, but very significant variability. Among these sources is the candidate. Z-source identified in Barnard et al. (2003, No. 966) and two Three ROSAT GlC candidates have more than one counterpart in the XMM LP-total catalogue. [SHL2001] 249 correlates 24 In addition [SHL2001] 258 correlates with No. 1275, No. 1289 with sources No. 1262 and No. 1267, where the latter is the X- and No. 1293. However these sources have each an additional ROSAT ray counterpart of the globular cluster B 185. [SHL2001] 254 counterpart.

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Several sources identified with globular clusters in previous studies have counterparts in the XMM LP-total catalogue but are not classified as GlC sources by us. Source No. 403 ([SHL2001] 74) correlates with B 007, which is now identified as a background galaxy (Caldwell et al. 2009; Kim et al. 2007, RBC V3.5). Sources No. 793 ([SHL2001] 136, s1-12) and No. 796 (s1-11) are the X-ray counterparts of B 042D and B 044D, respectively, which are also suggested as background objects by Caldwell et al. (2009). Source No. 948 (s1-83) correlates with B 063D, which is listed as a globular cluster candidate in RBC V3.5, but might be a foreground star (Caldwell et al. 2009). Due to this ambiguity in classification we classified the source as hard . Source No. 966 correlates with [SHL2001] 184, which was classified as the counterpart of the globular cluster NB 21 (RBC V3.5) in the ROSAT PSPC survey (SHL2001). In addition, source No. 966 also correlates with the Chandra source r2-26 (Kong et al. 2002b). Due to the much better spatial resolution of Chandra compared to ROSAT, Kong et al. (2002b) showed that source r2-26 does not correlate with the globular cluster NB 21. Barnard et al. (2003) identified this source as the first Z-source in M 31. The nature of

Fig. 33. The distribution of (V−I)0 for globular clusters (and candidates) source No. 1078 is unclear as RBC V3.5 reported that source from the RBC V4, located in the XMM LP-total field. to be a foreground star, while Caldwell et al. (2009) classified it as an old globular cluster. Due to this ambiguity in the classification and due to the fact that source No. 1078 is resolved of the sources discussed in Barnard et al. (2008, No. 1057, into two Chandra sources (r2-9, r2-10), we decided to classify No. 1692). the source as hard . Due to the transient nature (Kong et al. The 18 X-ray sources correlating with globular clusters 2002b; Williams et al. 2006b) and the ambiguous classifica- which were found in the ROSAT HRI observations (PFJ93) were tions reported by RBC V3.5 (GlC) and Caldwell et al. (2009, all re-detected in the XMM-Newton data. HII region), we adopt the classification of PFH2005 ( XRB ) From the numerous studies of X-ray globular cluster coun- for source No. 1152. SBK2009 classified the source correlating terparts in M 31 based on Chandra observations (Kong et al. with source No. 1293 as a globular cluster candidate. We are not 2002b; Di Stefano et al. 2002; Williams et al. 2004; Trudolyubov able to confirm this classification, as none of the globular clus- & Priedhorsky 2004; Voss & Gilfanov 2007), only eight sources ter catalogues used, contains an entry at the position of source are undetected in the present study. One of them ([TP2004] 1) is No. 1293. Instead we found a radio counterpart in the catalogues located far outside the field of M 31 covered by the Deep XMM- of Gelfand et al. (2005), Braun (1990) and NVSS. We therefore Newton Survey. The transient nature of [TP2004] 35, and the fact classified the source as an AGN candidate, as was also done in that it is not observed in any XMM-Newton observation taken be- PFH2005. fore December 2006 was mentioned in Sect. 7.2. The six remain- For source No. 1449 ([SHL2001] 289) the situation is more ing sources (r2-15, r3-51, r3-71, [VG2007] 58, [VG2007] 65, complicated. SHL2001 report [MA94a] 380 as the globular clus- [VG2007] 82) are located in the central area of M 31 and are ter correlating with this X-ray source. Based on the same refer- also not reported in PFH2005. Figure 34 shows the position of ence, Fan et al. (2005) included the optical source in their sta- these six sources (in red) and the sources of the XMM LP-total tistical study of globular cluster candidates. However, the paper catalogue (in yellow). If the brightness of the six sources had with the acronym [MA94a] is not available. An intensive liter- not changed between the Chandra and XMM-Newton observa- ature search of the papers by Magnier did not reveal any work tions, they would be in principle bright enough to be detected relating to globular clusters in M 31, apart from Magnier (1993) by XMM-Newton in the merged observations of the central field, which is cited in Fan et al. (2005) as “MIT”. In addition the which have in total an exposure ∼>100 ks. Two sources (r2-15 and source is not included in any other globular cluster catalogues [VG2007] 65) are located next to sources detected by XMM- listed in Sect. 3.8. In the X-ray studies of Williams et al. (2004) Newton. Source r2-15 is located within 13 of No. 1012 and and PFH2005 and in Magnier et al. (1992) the source is classi- within 17 of No. 1017 and has – in the Chandra observation fied as a foreground star (candidate). Hence, we also classified – a similar luminosity to both XMM-Newton sources. The dis- source No. 1449 as a foreground star candidate, but suggest opti- tance between No. 1012 and No. 1017 is 17 and within 20 cal follow-up observations of the source to clarify its true nature. of No. 1012, XMM-Newton detected source No. 1006, which A similar case is source No. 422 ([SHL2001] 76), which is is about a factor 4.6 fainter than No. 1012. Therefore, when classified as a globular cluster by SHL2001, based on a corre- in a bright state, source r2-15 should be detectable with XMM- lation with [MA94a] 16. Here again the source is not listed in Newton. Source [VG2007] 65 is located within 17of No. 1100, any of the globular cluster catalogues used. We found one cor- which is at least 3.5 times brighter than [VG2007] 65. This may relation of source No. 422 with an object in the USNO-B1 cat- complicate the detection of [VG2007] 65 with XMM-Newton. alogue, which has no B2 and R2 magnitude. Two faint sources The variability of [VG2007] 58, [VG2007] 65, and [VG2007] 82 (V > 22.5 mag) of the LGGS catalogue are located within the is supported by the fact that these three sources were not detected X-ray positional error circle. Thus source No. 422 is classified in any Chandra study, prior to Voss & Gilfanov (2007). Hence, as hard . While RBC V3.5 classified the optical counterpart of these six sources are likely to be at least highly variable or even source No. 1634 ([SHL2001] 316) as a globular cluster candi- transient. date, Caldwell et al. (2009) regard SK 182C as being a source

A55, page 38 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

1212 976 942 862 1092 936 1191 1118 1022 984 r3-51 1115 1076 907 804 766 838 1194 1137 952 924 859 923 224 1134 1102 921 895 1152 1060 1180 1084 972 4 1078 829 1144 1041 11671160 11361122 944 798 12031195 1006 82 836823 17,r2-151012 58 807 1216 1017 883 840 795 1131 1172 110065 1059 820 104610241005985 10231015 940922 1124 1103 1075 1010990 966 870 10501034 994971 1061 1033 997 877 1116 1093 1036 981 783 810 1157 992 76 968 1025 872 1016 879 855 1108 960 888 974 876 788 1000 930 1214 1056 1199 1146 816800 1101 835 993 911 871 853 11141096 10281011 1013 1176 791 1189 1091 10481032 1110 819 Fig. 34. Image of the central field of M 31 28,r3-71 975 797 over-plotted with the positions of six possible 1117 957 910 transient sources (red) and the sources of the 782 XMM LP-total catalogue. Sources r2-15 and 1105 r3-71 are listed as sources #17 and #28, respec- 5 arcmin tively, in Di Stefano et al. (2002). The three 26 1051 “red” sources that are only marked with a num- 1149 878 1171 863 ber (#58, #65, #82) are taken from Vos s & 979 1 935 814 Gilfanov (2007). of unknown nature. Therefore we decided to classify source located in the outskirts of the central field could not have been No. 1634 as hard . detected as variable in the study presented in SPH2008, as they only showed variability with a significance >3σ between the archival and the “Large Project” observations. For 69 sources the 11. Conclusions flux varied by more than a factor of five between XMM-Newton observations; ten of these varied by a factor >100. This paper presents the analysis of a large and deep XMM- Newton survey of the bright Local Group SA(s)b galaxy M 31. Discrepancies in source detection between the Large XMM- The survey observations were taken between June 2006 and Newton Survey catalogue and previous XMM-Newton catalogues February 2008. Together with re-analysed archival observations, could be explained by different search strategies, and differences they provide full coverage for the first time of the M 31 D25 el- in the processing of the data, in the parameter settings of the ∼ 35 −1 lipse down to a 0.2–4.5keV luminosity of 10 erg s . detection runs and in the software versions used. Correlations The analysis of combined and individual observations al- with previous Chandra studies showed that those sources not lowed the study of faint persistent sources as well as brighter detected in this study are strongly time variable, transient, or un- variable sources. The source catalogue of the Large XMM- resolved. This is particularly true for sources located close to the Newton Survey of M 31 contains 1897 sources in total, of centre of M 31, where Chandra’s higher spatial resolution re- which 914 sources were detected for the first time in X-rays. solves more sources. Some of the undetected sources from pre- 34 −1 The XID source luminosities range from ∼4.4 × 10 erg s to vious ROSAT studies were located outside the field covered with 38 −1 2.7 × 10 erg s . The previously found differences in the spa- XMM-Newton. However, there were several sources detected by > 37 −1 tial distribution of bright (∼10 erg s ) sources between the ROSAT that had a ROSAT detection likelihood higher than 15. northern half and southern half of the disc could not be con- If these sources were still in a bright state they should have been firmed. The identification and classification of the sources was detected with XMM-Newton. Thus, the fact that these sources are based on properties in the X-ray wavelength regime: hardness not detected with XMM-Newton implies that they are transient ratios, extent and temporal variability. In addition, information or at least highly variable sources. On the other hand 242 hard obtained from cross correlations with M 31 catalogues in the ra- XMM-Newton sources were found with XID fluxes higher than dio, infra-red, optical and X-ray wavelength regimes were used. 10−14 erg cm−2 s−1, which were not detected with ROSAT. The source catalogue contains 12 sources with spatial extent between 6. 2 and 23. 0. From spectral investigation and compar- To study the properties of the different source populations ison with optical images, five sources were classified as galaxy of M 31, it was necessary to separate foreground stars (40 plus cluster candidates. 223 candidates) and background sources (11 AGN and 49 can- Out of 1407 examined sources 317 showed long term vari- didates, four galaxies and 19 candidates, one galaxy cluster and ability with a significance >3σ between the XMM-Newton obser- five candidates) from the sources of M 31. 1247 sources could vations. These include 173 sources in the disc that were not cov- only be classified as hard , while 123 sources remained without ered in the study of the central field (SPH2008). Three sources identification or classification. The majority (about two-thirds,

A55, page 39 of 51 A&A 534, A55 (2011) see Stiele et al. 2011, in prep.) of sources classified as hard are Technologie/Deutsches Zentrum für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 expected to be background objects, especially AGN. OR 0405). The catalogue of the Large XMM-Newton survey of M 31 contains 30 SSS candidates, with unabsorbed 0.2–1.0 keV luminosities between 2.4 × 1035 erg s−1 and 2.8 × 1037 erg s−1. SSSs References are concentrated to the centre of M 31, which can be explained Antoniou, V., Zezas, A., Hatzidimitriou, D., & Kalogera, V. 2010, ApJ, 716, by their correlation with optical novae, and by the overall spatial L140 distribution of M 31 late type stars (i.e. enhanced density towards Bałucinska-Church,´ M., & McCammon, D. 1992, ApJ, 400, 699 Barmby, P., McLaughlin, D. E., Harris, W. E., Harris, G. L. H., & Forbes, D. A. the centre). Of the 14 identifications made of optical novae, four 2007, AJ, 133, 2764 were presented in more detail. Barnard, R., Kolb, U., & Osborne, J. P. 2003, A&A, 411, 553 The 25 identified and 31 classified SNRs had XID luminosi- Barnard, R., Stiele, H., Hatzidimitriou, D., et al. 2008, ApJ, 689, 1215 ties between 1.1 × 1035 erg s−1 and 4.3 × 1036 erg s−1. Three of Bender, R., Kormendy, J., Bower, G., et al. 2005, ApJ, 631, 280 the 25 identified SNRs were detected for the first time in X-rays. Block, D. L., Bournaud, F., Combes, F., et al. 2006, Nature, 443, 832 Bonfini, P., Hatzidimitriou, D., Pietsch, W., & Reig, P. 2009, A&A, 507, 705 For one SNR the ROSAT classification can be confirmed. Six of Bowyer, S., Margon, B., Lampton, M., & Cruddace, R. 1974, ApJ, 190, 285 the SNR candidates were selected from correlations with sources Brandt, W. N., & Hasinger, G. 2005, ARA&A, 43, 827 in SNR catalogues from the literature. As these six sources had Braun, R. 1990, ApJS, 72, 761 rather “hard” hardness ratios they are good candidates for “ple- Braun, R., & Walterbos, R. A. M. 1993, A&AS, 98, 327 Brusa, M., Zamorani, G., Comastri, A., et al. 2007, ApJS, 172, 353 rions”. An investigation of the spatial distribution showed that Caldwell, N., Harding, P., Morrison, H., et al. 2009, AJ, 137, 94 most SNRs and candidates are located in regions of enhanced Cash, W. 1979, ApJ, 228, 939 star formation, especially along the 10 kpc dust ring in M 31. Cavaliere, A., & Fusco-Femiano, R. 1976, A&A, 49, 137 This connection between SNRs and star forming regions, im- Colbert, E. J. M., Heckman, T. M., Ptak, A. F., Strickland, D. K., & Weaver, plies that most of the remnants are from type II supernovae. Most K. A. 2004, ApJ, 602, 231 Collura, A., Reale, F., & Peres, G. 1990, ApJ, 356, 119 of the SNR classifications from previous studies have been con- Condon, J. J., Cotton, W. D., Greisen, E. W., et al. 1998, AJ, 115, 1693 firmed. However, in five cases these classifications are doubtful. Cox, A. 2001, Allen’s astrophysical quantities (Springer) The population of “hard” M 31 sources mainly consists Crampton, D., Hutchings, J. B., Cowley, A. P., Schade, D. J., & van Speybroeck, of XRBs. These rather bright sources (XID luminosity range: L. P. 1984, ApJ, 284, 663 × 36 −1 × 38 −1 Di Stefano, R., Kong, A. K. H., Garcia, M. R., et al. 2002, ApJ, 570, 618 1.0 10 erg s to 2.7 10 erg s ) were selected from their Di Stefano, R., Kong, A. K. H., Greiner, J., et al. 2004, ApJ, 610, transient nature or strong long term variability (variability factor 247 (DKG2004) >10; ten identified, 26 classified sources). The spectral proper- Dodorico, S., Dopita, M. A., & Benvenuti, P. 1980, A&AS, 40, 67 ties of three transient sources were presented in more detail. Dubath, P., & Grillmair, C. J. 1997, A&A, 321, 379 A sub-class of LMXBs is located in globular clusters. They Eger, P. 2008, Diploma thesis, TU München Fabbiano, G. 2006, ARA&A, 44, 323 were selected from correlations with optical sources included in Fan, Z., Ma, J., Zhou, X., et al. 2005, PASP, 117, 1236 globular cluster catalogues (36 identified, 16 classified sources). Filipovic,´ M. D., Haberl, F., Winkler, P. F., et al. 2008, A&A, 485, 63 The XID luminosity of GlCs ranges from 2.3 × 1035 erg s−1 to Freyberg, M. J., Briel, U. G., Dennerl, K., et al. 2004, in X-Ray and Gamma-Ray 1.0 × 1038 erg s−1. The spatial distribution of this source class Instrumentation for Astronomy XIII., ed. K. A. Flanagan, & O. H. W. Siegmund, Proc. SPIE, 5165, 112 also showed an enhanced concentration to the centre of M 31. Gaetz, T. J., Blair, W. P., Hughes, J. P., et al. 2007, ApJ, 663, 234 From optical and X-ray colour-colour diagrams possible Galache, J. L., Garcia, M. R., Steeghs, D., et al. 2007, The Astronomer’s HMXB candidates were selected. If the sources were bright Telegram, 1147, 1 enough, an absorbed power-law model was fitted to the source Galleti, S., Federici, L., Bellazzini, M., Fusi Pecci, F., & Macrina, S. 2004, A&A, spectra. Two of the candidates had a photon index consistent 416, 917 Galleti, S., Bellazzini, M., Federici, L., & Fusi Pecci, F. 2005, A&A, 436, 535 with the photon index range of NS HMXBs. Hence these two Galleti, S., Federici, L., Bellazzini, M., Buzzoni, A., & Fusi Pecci, F. 2006, sources were suggested as new HMXB candidates. A&A, 456, 985 Follow-up studies in the optical as well as in radio are in Galleti, S., Bellazzini, M., Federici, L., Buzzoni, A., & Fusi Pecci, F. 2007, progress or are planned. They will allow us to increase the A&A, 471, 127 Galleti, S., Bellazzini, M., Buzzoni, A., Federici, L., & Fusi Pecci, F. 2009, number of identified sources and help us to classify or iden- A&A, 508, 1285 tify sources which can up to now only be classified as hard Garcia, M. R., Murray, S. S., Primini, F. A., et al. 2000, ApJ, 537, L23 or are without any classification. This work focused on the over- Gelfand, J. D., Lazio, T. J. W., & Gaensler, B. M. 2004, ApJS, 155, 89 all properties of the source population of individual classes and Gelfand, J. D., Lazio, T. J. W., & Gaensler, B. M. 2005, ApJS, 159, 242 gave us deeper insights into the long-term variability, spatial and Ghavamian, P., Blair, W. P., Long, K. S., et al. 2005, AJ, 130, 539 Giacconi, R., Murray, S., Gursky, H., et al. 1974, ApJS, 27, 37 flux distribution of the sources in the field of M 31 and thus Green, D. A. 2009, BASI, 37, 45 helped us to improve our understanding of the X-ray source pop- Grimm, H., Gilfanov, M., & Sunyaev, R. 2002, A&A, 391, 923 ulation of M 31. Haberl, F., & Pietsch, W. 1999, A&A, 344, 521 Hasinger, G., Altieri, B., Arnaud, M., et al. 2001, A&A, 365, L45 Acknowledgements. This publication makes use of the USNOFS Image Hatzidimitriou, D., Pietsch, W., Misanovic, Z., Reig, P., & Haberl, F. 2006, and Catalogue Archive operated by the United States Naval Observatory, A&A, 451, 835 Flagstaff Station (http://www.nofs.navy.mil/data/fchpix/), of data Henze, M., Pietsch, W., Haberl, F., et al. 2009a, A&A, 500, 769 products from the Two Micron All Sky Survey, which is a joint project of Henze, M., Pietsch, W., Sala, G., et al. 2009b, A&A, 498, L13 the University of Massachusetts and the Infrared Processing and Analysis Hodge, P. W., Krienke, O. K., Bellazzini, M., et al. 2009, AJ, 138, 770 Center/California Institute of Technology, funded by the National Aeronautics Holland, S. 1998, AJ, 115, 1916 and Space Administration and the National Science Foundation, of the SIMBAD Kaaret, P. 2002, ApJ, 578, 114 database, operated at CDS, Strasbourg, France, and of the NASA/IPAC Kahabka, P. 1999, A&A, 344, 459 Extragalactic Database (NED) which is operated by the Jet Propulsion Kahabka, P., & van den Heuvel, E. P. J. 1997, ARA&A, 35, 69 Laboratory, California Institute of Technology, under contract with the National Kang, Y., Bianchi, L., & Rey, S. 2009, ApJ, 703, 614 Aeronautics and Space Administration. The XMM-Newton project is supported Kim, S. C., Lee, M. G., Geisler, D., et al. 2007, AJ, 134, 706 by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum Kimball, A. E., & Ivezic,´ Ž. 2008, AJ, 136, 684 für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OX 0001) and the Max-Planck Kong, A. K. H., Garcia, M. R., Primini, F. A., & Murray, S. S. 2002a, ApJ, 580, Society. HS acknowledges support by the Bundesministerium für Wirtschaft und L125

A55, page 40 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

Kong, A. K. H., Garcia, M. R., Primini, F. A., et al. 2002b, ApJ, 577, 738 Schmitt, J. H. M. M. 2000, in ed. R. E. Schielicke, Rev. Mod. Astron., 13, 115 Kong, A. K. H., Sjouwerman, L. O., Williams, B. F., Garcia, M. R., & Dickel, Sharov, A. S., & Alksnis, A. 1998, Astron. Lett., 24, 641 J. R. 2003, ApJ, 590, L21 Shaw Greening, L., Barnard, R., Kolb, U., Tonkin, C., & Osborne, J. P. 2009, Kotov, O., Trudolyubov, S., & Vestrand, W. T. 2006, ApJ, 641, 756 A&A, 495, 733 (SBK2009) Krienke, O. K., & Hodge, P. W. 2007, PASP, 119, 7 Skrutskie, M. F., Cutri, R. M., Stiening, R., et al. 2006, AJ, 131, 1163 Krienke, O. K., & Hodge, P. W. 2008, PASP, 120, 1 Smirnova, O., Alksnis, A., & Zharova, A. V. 2006, Information Bulletin on Long, K. S., Blair, W. P., Winkler, P. F., et al. 2010, ApJS, 187, 495 Variable Stars, 5737, 1 Maccacaro, T., Gioia, I. M., Wolter, A., Zamorani, G., & Stocke, J. T. 1988, ApJ, Stanek, K. Z., & Garnavich, P. M. 1998, ApJ, 503, L131 326, 680 Stark, A. A., Gammie, C. F., Wilson, R. W., et al. 1992, ApJS, 79, 77 Magnier, E. A. 1993, Ph.D. Thesis, Massachusetts Inst. of Tech. Stiele, H., Pietsch, W., Haberl, F., Freyberg, M., & Trigo, M. D. 2007, The Magnier, E. A., Lewin, W. H. G., van Paradijs, J., et al. 1992, A&AS, 96, 379 Astronomer’s Telegram, 1191, 1 Magnier, E. A., Prins, S., van Paradijs, J., et al. 1995, A&AS, 114, 215 Stiele, H., Pietsch, W., Haberl, F., & Freyberg, M. 2008, A&A, 480, Massey, P., Olsen, K. A. G., Hodge, P. W., et al. 2006, AJ, 131, 2478 599 (SPH2008) Massey, P., McNeill, R. T., Olsen, K. A. G., et al. 2007, AJ, 134, 2474 Stiele, H., Pietsch, W., Haberl, F., et al. 2010, Astron. Nachr., 331, 212 McClintock, J. E., & Remillard, R. A. 2006, Black hole binaries, ed. W. H. G. Supper, R., Hasinger, G., Pietsch, W., et al. 1997, A&A, 317, 328 Lewin, & M. van der Klis (Cambridge University Press), 157 Supper, R., Hasinger, G., Lewin, W. H. G., et al. 2001, A&A, 373, A63 Meusinger, H., Henze, M., Birkle, K., et al. 2010, A&A, 512, A1 Trinchieri, G., & Fabbiano, G. 1991, ApJ, 382, 82 (TF91) Misanovic, Z., Pietsch, W., Haberl, F., et al. 2006, A&A, 448, 1247 Trudolyubov, S., & Priedhorsky, W. 2004, ApJ, 616, 821 Monet, D. G., Levine, S. E., Canzian, B., et al. 2003, AJ, 125, 984 Trudolyubov, S. P., & Priedhorsky, W. C. 2008, ApJ, 676, 1218 Mould, J., Barmby, P., Gordon, K., et al. 2008, ApJ, 687, 230 Trudolyubov, S., Priedhorsky, W., Borozdin, K., Mason, K., & Cordova, F. 2002, Mushotzky, R. F., Cowie, L. L., Barger, A. J., & Arnaud, K. A. 2000, Nature, IAU Circ., 7798, 2 404, 459 Trudolyubov, S., Priedhorsky, W., & Cordova, F. 2006, ApJ, 645, 277 (TPC06) Nedialkov, P., Orio, M., Birkle, K., et al. 2002, A&A, 389, 439 Urry, C. M., & Padovani, P. 1995, PASP, 107, 803 Orio, M. 2006, ApJ, 643, 844 van den Heuvel, E. P. J., Bhattacharya, D., Nomoto, K., & Rappaport, S. A. 1992, Orio, M., Nelson, T., Bianchini, A., Di Mille, F., & Harbeck, D. 2010, ApJ, 717, A&A, 262, 97 739 van Speybroeck, L., Epstein, A., Forman, W., et al. 1979, ApJ, 234, L45 Osborne, J. P., Borozdin, K. N., Trudolyubov, S. P., et al. 2001, A&A, 378, 800 Verbunt, F., & van den Heuvel, E. P. J. 1995, in X-ray binaries, ed. W. H. G. Pietsch, W. 2010, Astron. Nachr., 331, 187 Lewin, J. van Paradijs, & E. P. J. van den Heuvel (Cambridge University Pietsch, W., & Haberl, F. 2005, A&A, 430, L45 (PH2005) Press), 457 Pietsch, W., Misanovic, Z., Haberl, F., et al. 2004, A&A, 426, 11 Voss, R., & Gilfanov, M. 2007, A&A, 468, 49 Pietsch, W., Fliri, J., Freyberg, M. J., et al. 2005a, A&A, 442, 879 (PFF2005) Voss, R., Pietsch, W., Haberl, F., et al. 2008, A&A, 489, 707 Pietsch, W., Freyberg, M., & Haberl, F. 2005b, A&A, 434, 483 (PFH2005) Walterbos, R. A. M., & Braun, R. 1992, A&AS, 92, 625 Pietsch, W., Burwitz, V., Greiner, J., et al. 2006, The Astronomer’s Telegram, Walterbos, R. A. M., Brinks, E., & Shane, W. W. 1985, A&AS, 61, 451 850, 1 Watson, M. G., Schröder, A. C., Fyfe, D., et al. 2009, A&A, 493, 339 Pietsch, W., Haberl, F., Sala, G., et al. 2007, A&A, 465, 375 Wheelock, S. L., Gautier, T. N., Chillemi, J., et al. 1994, NASA STI/Recon Pooley, G. G. 1969, MNRAS, 144, 101 Technical Report N, 95, 22539 Primini, F. A., Forman, W., & Jones, C. 1993, ApJ, 410, 615 (PFJ93) Williams, B. F., Garcia, M. R., Kong, A. K. H., et al. 2004, ApJ, 609, 735 Quimby, R. M. 2006, Ph.D. Thesis, University of Texas at Austin Williams, B. F., Garcia, M. R., Kong, A. K. H., Primini, F. A., & Murray, S. S. Quimby, R., Mondol, P., Hoeﬂich, P., Wheeler, J. C., & Gerardy, C. 2005, The 2005a, ApJ, 620, 723 Astronomer’s Telegram, 600, 1 Williams, B. F., Garcia, M. R., McClintock, J. E., Primini, F. A., & Murray, S. S. Read, A. M., Sembay, S. F., Abbey, T. F., & Turner, M. J. L. 2006, in The X-ray 2005b, ApJ, 632, 1086 Universe 2005, ed. A. Wilson, ESA SP, 604, 925 Williams, B. F., Garcia, M. R., McClintock, J. E., Primini, F. A., & Murray, S. S. Revnivtsev, M., Sazonov, S., Gilfanov, M., Churazov, E., & Sunyaev, R. 2006, 2006a, ApJ, 637, 479 (WGM06) A&A, 452, 169 Williams, B. F., Naik, S., Garcia, M. R., & Callanan, P. J. 2006b, ApJ, 643, 356 Rich, R. M., Corsi, C. E., Cacciari, C., et al. 2005, AJ, 129, 2670 Wilms, J., Allen, A., & McCray, R. 2000, ApJ, 542, 914 Sarajedini, A., Barker, M. K., Geisler, D., Harding, P., & Schommer, R. 2007, Yan, M., Sadeghpour, H. R., & Dalgarno, A. 1998, ApJ, 496, 1044 AJ, 133, 290

A55, page 41 of 51 A&A 534, A55 (2011)

263 151 100 100 30:00 30:00 247 247 229 208 67 229 208 67 294 294 M 31 S3 159 138 M 31 S3 159 138 64 64 June 2006 308 236 July 2007 308 236 58 58 25:00326 230 76 32625:00 230 76 35 35 2 216196 216196 346325 6 346325 6 57 57 114 114 98 98 61 281 131 92 69 281 131 92 69 257 257 20:00 158 66 20:00 158 66 200 106 5 200 5 95 37 10 106 37 10 95 181 133 45 181 45 198 52 198 133 62 77 77 52 293286 102 286 102 80 27 293 80 27 119 119 32 32 284 220 23 284 220 23 321 321 214 14 8 214 14 8 15:00 155 135 63 15:00 155 135 63 233 44 34 233 44 34 280 154 280 154 205 50 42 205 50 42 338 7 338 7 301 152148 112 301 148 112 149 30 152 30 149 279 266 85 4 85 237 279 266 237 4 61 21 61 71 71 21 305 305 177 177 10:00 282 10:00 282 306 224 306 224 163 13 163 13 9089 20 9089 46 46 20 24 24 341 165 144 341 165 144 26 26 40 40 209 120 81 209 120 81 88 88 40:05:00 40:05:00 29 29 0.2 - 4.5 keV 60 0.2 - 4.5 keV 60 XMM-Newton XMM-Newton EPIC PN + MOS 49 EPIC PN + MOS 49 00:00.0 00:00 0:40:00 30 39:00 30 38:00 37:30 0:40:00 30 39:00 30 38:00 37:30

169 705 531 41 819 645 263 184 151 9 797 681 597 100 M 31416 S1 30:00 782 549 460 247 10:00 604 229 208 67 606 566 452January 2002 294 M 31 S3 442 878 615 159 138 750748 484 396 863 723 370 64 January 2008 935 814 736 668 599 308 236 826 589 439 336 965 483 58 696 25:00326 230 76 925912 799 567 542 320 05:00 684 507 393 611 436 35 933 685 612 314 372 216196 793 521 346325 6 57 644 29 114 302 841 726 675 588 350 304 98 421 361 131 92 69 934 532 353 281 257 796 690 673 608 79 1009 682 653 582 20:00 158 66 906 875 426 352 200 106 5 41:00:00 300 37 10 959 633 357337 95 1031 419 376 298 181 45 548 415 347333 198 133 52 590 362 77 286 102 3 949946 885 792 293 80 402 119 27 1052 772 513 463 072 32 961 830 356 374 284 220 23 843 535 321 904 601 474 319 14 1003 801 214 8 937 897 643 15:00 155 135 63 741 576 233 44 34 55:001001 29 280 154 822 555 466 205 50 42 071 747 636 338 7 744 392 377 301 148 112 070 553 389 152 30 846 309 149 833 279 266 85 4 995 811 603 472 237 581563 468 327 632 476453 61 21 674 640 607 557 305 71 809 323317 81 790 600 363 29 177 758 10:00 282 683 455 423 306 224 789 479 163 13 40:50:00 916 459 9089 20 948 457 373 46 842 1047 354 24 1008 887 761743 569 339 341 165 144 613 26 666 432 404 40 982 777 209 120 659 8881 40:05:00 941 764 368 45:00 881 383 0.2 - 4.5 keV 29 837 60 0.2 - 4.5909893 keV 710 658 598 XMM-Newton XMM-Newton 768 649 680 769 528 EPIC PN + MOS 49 0:40:00 30 39:00 30 38:00 37:30 EPIC PN30 + MOS 42:00 30 41:00 30 0:40: 771 728 648 511 Fig. A.1. Logarithmically scaled XMM-Newton EPIC low background images integrated in 2 × 2 pixels of the M 31 observations combining PN and MOS 1 and MOS 2 cameras in the (0.2–4.5) keV XID band. The data are smoothed with a 2D-Gaussian of FWHM 10, which corresponds to the point spread function in the centre area. The images are corrected for unvignetted exposures. Contours in units of 10−6 ct s−1 pix−1 including a factor of two smoothing are at (8, 16, 32, 64, 128) in the upper left panel,at(6, 8, 16, 32, 64, 128) in the upper right panel,andat (4, 8, 16, 32, 64, 128) in both lower panels. Sources from the XMM LP-total catalogue are marked as 60 × 60 squares.

A55, page 42 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

390 533 371 271 385 366 709 268 371 271 35:00 398 533 727 369 M 31 SS3 709 M 31 268 SS3 734 422 311 255243 35:00 398 378 727 369 448 342 312 July 2006 734 December311 255 2007 676 367 422 378 243 299 448 342 312 560 506 367 779 686 334 676 299 560 480 686 506 693 441429 330 779 334 716 443 427 394 263 184 480 522 430 693 441429 330 30:00 473 443 427 263 184 81 525 406 247 716 522 394 667 340 208 802 473 430 725 503 229 30:00 424414 781 667 525 406 340 247 401 294 725 229 208 552 503 424414 701 294 328 552 401 692 387 331 701 642625 437 328 308 236 692 387 331 778 642625 437 714 450 308 236 85 25:00 572 326 230 778 714 450 470 25:00785 572 326 230 620 538 425 446 372 196 470 704 592 554 346 216 546 514 325 620 538 425 595 510 446 372 216196 745 704 592 554 514 346 526 498 546 510 325 638 551 745 595 497 498 361 281 638 551 526 537 456 257 497 158 361 20:00 520518 200 281 646 537 456 257 40:20:00 520518 200 571 181 646 198 593 362 571 181 493 293286 198 417400 477 433 593 493 362 286 465 417 293 737 689 469 374 284 220 477 400 579 321 465 433 629 562 409 214 469 374 284 737 689 579 220 15:00 568 409 321 233 629 562 214 663 280 15:00 568 205 586 395 338 663 233 622 301 280 431 586 395 338 205 490 622 301 583 482462 279 266 237 431 490 540 583 482462 279 266 237 381 305 540 40:10:00 282 305 306 381 0.2 - 4.5 keV 10:00 282 478 0.2 - 4.5 keV 306 XMM-Newton 478 341 XMM-Newton EPIC PN + MOS 341 EPIC PN + MOS 42:00 30 41:00 30 0:40:00 39:30 42:00 30 41:00 30 0:40:00 39:30 995 811 995 833811 674 640632 607 809 674 632 607 1187 790 M 31 SS2 640 600 1187 809 758 683 790 600 50:00 916 789 July 2006 758 683 1196 11631139 948 916 789 1241 1140 1074 50:00 1196 M 31 SS2 842 1241 11631139 948 1047 1140 1074 842 1188 1008 761743 569 1047 December 2007 613 1188 761 569 666 1008 743 613 982 777 666 258 659 982 777 1258 11301111 659 941 764 11301111 45:00 881 941 764 1026 837 45:00 881 1211 969 710 1026 837 909893 1211 969 598 909893 710 938 598 1208 1073 768 649 938 1027 680 528 1208 1073 768 649 951 769 1027 680 1145 956 951 769 528 1145 956 1155 831 771 728 648 40:40:00 973 1155 728 858 40:40:00 973 831 771 648 10821064 964 756 858 756 1202 998 679 10821064 964 11291120 1202 998 679 825815 1030 11291120 825 943 847 735 707 500 1030 815 742 943 847 735 707 500 721 742 533 721 892 844 787 709 533 1174 892 844 35:0012371229 908 754 1174 787 709 727 12371229 908 754 1054 903 734 35:00 727 913 834 780 1054 903 734 1164 955 851 767 913 834 780 676 1164 851 928 899 560 955 767 676 817 506 928 899 779 686 560 506 817 686 926 852 480 779 693 926 852 48 716 522 693 828805802 716 30:00 1169 954 873 828805 522 889 781 667 525 30:00 954 802 725 1169 889873 781 667 525 902 725 880 552 902 701 880 552 701 692 642625 692 901 642 1088 778 625 901 778 0.2 - 4.5 keV 714 572 1088 25:00 866 785 0.2 - 4.5 keV 714 25:00 866 785 572 XMM-Newton 620 XMM-Newton 704 620 704 EPIC PN + MOS 745 EPIC PN + MOS 745 30 43:00 30 42:00 30 0:41:00 30 43:00 30 0:42:00 30 41:00

Fig. A.1. continued. Contours are at (4, 8, 16, 32, 64, 128) in the upper left panel and lower right panel,at(6, 8, 16, 32, 64, 128) in the upper right panel,andat(8, 16, 32, 64, 128) in the lower left panel.

A55, page 43 of 51 A&A 534, A55 (2011)

1299 95 1385 10:00 1447 1240 10:00 1447 1240 1439 1105 1105 1266 M 31 SS1 1439 M 31 SS1 1363 1226 1266 1238 1051 878 1363 12381226 1051 1432 11711149 1149 878 1484 979July 2007863 1432 1171 863 June 2006 1342 1303 1252 935 1484 1303 979 1376 1231 1045 1376 1342 12521231 1045 935 1333 1333 1210 826 1210 826 1476 1412 965 1476 1412 965 1438 1233 1053 799 1438 1233 10861085 925912 1053 925912 799 05:001506 1366 1506 1085 1422 1288 1183 05:00 1366 1183 1448 933 1448 1422 1288 933 1431 12501242 1148 1431 12501242 1148 1456 793 1456 793 1260 1260 1459 1301 1087 841 1459 1301 1087 841 1454 1346 1276 1165 1454 1346 1276 1329 1284 934 796 1329 1165 934 531 1009 1284 796 1079 906 1 1079 1009 1206 1151 875 906 41:00:001483 1374 1095 1483 1206 1151 875 1341 1245 1162 959 41:00:00 1374 1341 1162 1095 1031 1245 1031 959 12181207 1207 949 1218 1490 1246 1083 946 885 792 1490 1083 949 885 1052 1246 946 792 1394 12921290 772 1394 1292 1052 772 14241396 1112 1072 1290 1112 961 843830 14241396 1072 961 830 843 1455 1353 1170 1003 904 801 1455 1353 1170 904 801 1318 937 897 1318 1003 897 14071397 1279 1407 1279 937 1398 12801269 1209 1181 13981397 1280 1209 55:00 55:00 1269 1181 1377 1350 1001 822 1350 1001 1352 1071 1377 1352 822 1071 1475 1326 1070 846 1475 1326 1070 846 1445 995 833811 1445 833 1491 1381 1311 1491 1311 995 811 1368 1259 1221 1368 1221 1402 1345 1089 1402 1345 1259 1383 809 809 1464 1187 790 1464 1187 1395 1322 1395 1322 790 916 789 789 50:00 1196 50:00 916 12541241 11631139 948 1196 11631139 948 1140 1074 842 12541241 1140 1074 1444 1364 1317 1047 1444 1364 842 1317 1047 1188 887 1188 1008 1008 13341310 1334 1178 982 982 1335 1258 1335 1258 11301111 1130 1321 941 1321 1111 941 40:45:00 881 40:45:00 881 1026 1026 1211 969 1211 969 909893 909893 0.2 - 4.5 keV 0.2 - 4.5 keV 938 938 1208 1073 1208 1073 XMM-Newton 1027 XMM-Newton 1027 951 951 1145 1145 EPIC PN + MOS 1155 EPIC PN + MOS 1155 40:00 40:00 30 44:00 30 43:00 30 0:42:00 30 0:44:00 30 43:001082 30 42:00 1082 1202 1253 1110 11891176 1032 975 11101091 1048 1285 1117 957 1253 975 1385 1299 1285 1117 1299 957 10:00 1447 1240 1385 1439 1105 M 31 SS1 10:00 1447 1240 M 31 SS1 1266 1105 1363 12381226 1051 1439 1149 January 2008878 1266 1432 1171 863 1363 12381226 1051 February 2008 1484 1303 979 1149 878 1376 1342 12521231 1045 935 1484 1432 1171 863 1303 1252 979 935 1333 1210 826 1376 1342 1231 1045 1476 965 1333 1210 826 1438 1233 1053 1476 965 925912 799 1438 1233 1506 1085 1053 799 05:00 1366 1183 1085 925912 1448 1422 1288 933 05:00 1506 1366 12501242 1422 1288 1183 1456 1431 1148 793 1448 933 1431 12501242 1148 1260 1456 793 556 1260 1301 1087 841 1459 1346 1556 61 1454 1276 1165 1459 1301 1087 841 1329 1284 934 796 1561 1454 1346 1276 1531 1009 1329 1165 934 1079 906 1284 796 555 1206 1151 875 1531 1009 41:00:00 1483 1374 1095 1079 906 1341 1245 1162 959 1555 1483 1206 1151 875 1031 41:00:00 1374 1341 1162 1095 1245 1031 959 12181207 949 1490 1246 1083 946 885 792 12181207 1052 949 1394 12921290 77 1490 1246 1083 946 885 79 14241396 1112 1072 961 1394 1292 1052 843830 1290 1112 14241396 1072 961 830 1455 1353 1170 1003 904 801 843 1318 1279 937 897 1455 1353 1170 904 14071397 1280 1318 1003 801 1398 1269 1209 1181 1407 1279 937 897 55:00 1001 13981397 1280 1209 1377 1350 822 55:00 1269 1181 1352 1071 1350 1001 1377 1352 822 1475 1326 1070 846 1071 1445 833 1475 1326 1070 846 1491 1311 995 811 1368 1221 1445 995 833 1402 1345 1259 1491 1311 811 1368 1259 1221 1464 809 1402 1345 1187 790 809 1395 1322 1464 1187 1395 1322 79 916 789 50:00 1196 78 12541241 11631139 948 40:50:00 916 1444 1140 1074 842 1196 11631139 948 1364 1317 1047 12541241 1140 1074 1444 1364 1317 842 1188 1008 1047 1188 1334 1008 982 1334 1335 1258 982 1335 11301111 1258 1321 941 1130 40:45:00 881 1321 1111 941 1026 45:00 881 969 1026 1211 893 909 1211 969 0.2 - 4.5 keV 0.2 - 4.5 keV 909893 938 XMM-Newton 1208 1073 XMM-Newton 938 1027 1208 1073 951 1027 EPIC PN + MOS 1145 EPIC PN + MOS 951 30 0:44:00 301155 43:00 42:30 30 0:44:00 301145 43:00 42:30 40:00 1155 Fig. A.1. continued. Contours are at (8, 16, 32, 64, 128) in the upper left panel and lower right panel,at(4, 8, 16, 32, 64, 128) in the upper right panel,andat(16, 32, 64, 128) in the lower left panel.

A55, page 44 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

468 327 317 277 188 476453 363 219 423 323 277 479455 235 317 188 50:00 212 M 31 S2 363 M 31 S2 459457 479455 423 235 373 207 50:00 212 354 238 December 2006 459457 January 2002 129 373 207 569 339 354 238 432 201 129 404 179 569 339 432 201 404 179 147 313 265 232 195 147 182175173 94 313 265 195 45:00 383 123 232 213 157 182173 94 45:00 383 175 123 213 598 275 161 136 157 193 121 329 167 598 275 161 136 649 351 193 121 289 178 86 167 528 109 649 329 418 351 86 289 178 109 258 528 418 386 64840:00 139 118 258 648 386 40:00 139 118 140 91 91 412 349 251 116 140 99 500 390 295 260 218 115 412 349 251 116 206 122 99 385 366 244234 190 150 500 390 295 260 218 115 533 371 271 206 122 268 202 107 385 366 244234 190 150 398 533 371 271 40:35:00 162 202 107 369 268 422 311 255243 189 126 40:35:00 398 162 378 369 448 342 312 311 255 189 126 367 93 422 378 243 299 448 342 312 560 506 367 93 334 560 299 480 506 441429 330 169 334 443 427 184 522 394 263 151 480 429 330 169 473 430 100 443441 30:00 427 394 263 184 151 525 406 340 247 522 430 100 208 6 473 503 414 229 30:00 525 247 424 406 340 401 294 229 208 6 552 503 424414 159 138 294 328 552 401 387 331 159 138 437 328 625 308 236 387 331 625 437 450 308 236 25:00 572 326 230 450 470 25:00 572 326 230 0.2 - 4.5 keV538 425 470 554 446 372 216196 0.2 - 4.5 keV 546 514 346325 538 425 510 446 372 216196 XMM-Newton 554 514 346 526 498 XMM-Newton546 510 325 497 498 361 EPIC PN + MOS526 EPIC PN + MOS 456 281 257 30 41:00497 30 40:00 30 0:39:00 30 41:00 30 40:00 30 0:39:00 361 456 281 257 499 375365 530 444 30:00 621 403 651 449 382 564 M 31 SN1 722 656 407397 M 31 CXOM3 697678 527 647 494 461 315 375365 July 2006 July 2007 403 706 30:00 621 382 505 651 449 558 278 722 656 407397 324 647 759 541 461 315 739 617 447 25:00 467445 411 221 706 574 543 379 227 505 803 775 717 650 591 434 307 558 278 753 464 391 324 661 485 408 759 541 539 475 345 285 739 617 447 602 440 467445 221 677 618 501 25:00 411 733 698 671 570 545 519 249 574 543 379 227 804 766 488 75 717 650 591 434 307 838 534 410 343 1 753 464 391 435 380 688 639 573 661 485475 408 631 491 428420 539 345 285 687 316 290 203 618602 440 20:00 384 264 698677671 570 501 829 733 545 519 488 249 798 515 388 187 766 836823 544 534 410 343 180 807 669662655 239 435 380 594 547 458 688 639 573 840 795 628 508 631 491 428420 820 715 687 316 290 203 20:00 384 264 274 252 610 523 413 544 515 388 187 783 204 810 740 654 624 565 451 291 669662655 547 458 239 623 578 495 594 508 762 738 584 715 628 720 364 85515:00 587 529 335 210 274 788 730 559 516 344 610 252 399 348322 523 413 816800 634 596 3 740 654 565 291 204 835 512 486 624623 578 495 451 732 670 509 303 762 738 584 1 720 364 791 288 15:00 587 529 335 705 531 405 730 559 516 344 210 819 348322 797 681 645 358 634 596 399 170 597 269 512 486 416 732 670 509 303 782 549 460 359 318 248242231 176 10:00 604 288 360 332 310 261 705 531 405 606 566 452 250 171 442 681 645 358 615 228 597 269 750748 484 396 416 723 668 370 2 549 460 359 318 248242231 736 599 41:10:00 604 439 360 332 310 261 589 336 606 566 452 250 483 615 442 750 228 696 567 748 484 396 542 262 723 370 320 272 736 668 599 05:00 684 507 393 611 436 439 685 612 589 336 314 483 0.2 - 4.5 keV 521 273 253 0.2 - 4.5696 keV 644 567 542 272 262 292 507 393 320 XMM-Newton 302 05:00 684 436 588 350 304 XMM-Newton685 611 421 612 314 532 353 521 273 253 608 EPIC PN + MOS 582 EPIC PN + MOS644 426 292 41:00:00 42:00 30 0:41:00 30350 40:00302 39:30 42:00 30 41:00419 30 0:40:00 39:30 588 304 421 353 Fig. A.1. continued. Contours are at (4, 8, 16, 32, 64, 128) in both upper panels and the lower left panel,andat(6, 8, 16, 32, 64, 128) in the lower right panel.

A55, page 45 of 51 A&A 534, A55 (2011)

399 170 364 15:00 335 303 344 210 348322 288 176 399 170 405 M 31 SN2 171 303 M 31 SN2 358 156 176 269 124 July 2006 288 416 405 460 359 318 248242231 171 January 2008 10:00 358 156 360 332 310 261 269 124 452 250 143 416 442 79 460 359 318 248242231 484 396 228 41:10:00 360 310 370 452 332 261250 143 442 79 439 73 484 396 228 483 336 197 142 370 199 113 134 439 73 272 262 215 336 142 507 393 320 145 483 197 05:00 436 199 113 141 48 67 134 314 166 542 262 215 521 273 253 223 507 320 272 145 168 74 55 05:00 436 393 141 48 222 314 292 226 521 166 350 302 246 273 253 223 168 74 55 304 245 172 108 96 32 421 353 287 103 54 222 241 211 38 292 226 72 350 302 246 426 259 304 108 96 352 254 186 146 110 421 353 245 172 103 54 41:00:00 300 174 532 287 241 38 357337 153 211 419 376 298 270 111101 72 415 347333 426 259 186 83 352 300 254 146 110 160 82 00:00 174 153 194 127 419 357337 270 111 402 68 548 376 347 298 101 513 463 192 33 415 333 83 356 160 82 5 117 75 194 319 276 128 402 127 68 474 513 463 192 33 225 132 39 267 356 117 75 535 319 276 128 55:00 466 240 474 225 132 39 392 377 185 267 389 105 55:00 309 51 555 466 240 472 191 62 392 377 185 468 327 553 389 105 476453 164 309 323 219 51 317 277 188 84 472 62 363 56 468 327 191 423 125 476453 164 479455 235 323 219 40:50:00459 212 53 317 277 188 84 457 363 56 373 207 423 125 354 479455 235 238 129 40:50:00 212 53 459457 339 87 78 373 207 432 404 201 354 179 238 129 339 87 78 0.2 - 4.5 keV 147 432 404 201 313 265 232 195 0.2 - 4.5 keV 179 182173 94 45:00XMM-Newton383 175 123 147 213 157 XMM-Newton 313 265 232 195 182175173 94 EPIC PN + MOS 275 161 136 45:00 383 123 193 EPIC PN + MOS 213 157 30329 0:40:00 30167 39:00 38:30 41:00 30 0:40:00 30 39:00 38:30 185 275 161 136 191 62 105 164 51 323 219 317 277 188 84 56 191 62 M 31 SN3 164 M 31 SN3 125 219 235 323 277 84 50:00 212 53 25 317 188 56 373 207 July 2006 125 December 2007 354 235 238 129 40:50:00 212 53 25 373 207 339 78 201 87 354 238 179 129 339 201 87 78 313 147 179 265 232 195 70 182173 83 45:00 175 94 147 123 313 265 195 213 157 65 232 70 182173 94 45:00383 175 123 275 161 136 28 213 193 121 22 157 65 329 167 351 86 275 161 136 28 289 178 109 193 121 22 329 167 36 351 258 289 178 86 6 418 109 40:40:00 139 118 36 11 258 91 16 386 140 2 40:00 139 118 18 11 349 251 116 43 16 99 12 140 91 295 260 218 115 18 2 206 122 17 3 412 349 251 116 43 85 366 244234 190 150 12 371 271 295 260 11599 107 47 1 390 218 268 202 31 206 122 3 385 366 244234 190 17 35:00 162 371 271 150 369 107 47 1 311 255 189 126 15 268 202 31 378 243 398 342 312 35:00 162 93 369 367 311 255 189 126 15 299 422 378 243 59 342 312 334 19 367 93 299 330 169 59 263 184 151 41 9 334 19 100 330 169 30:00 41 340 247 394 263 184 151 9 229 208 67 100 30:00 294 247 340 208 67 159 138 229 328 331 64 294 159 138 308 236 328 331 64 0.2 - 4.5 keV 58 25:00 230 76 0.2 - 4.5 keV308 236 58 XMM-Newton 35 25:00XMM-Newton 230 76 216196 EPIC PN + MOS 57 EPIC PN + MOS 35 0:40:00 30 39:00114 30 38:00 37:30 30 0:40:00216 30196 39:00 30 38:00 98 57 Fig. A.1. continued. Contours are at: (8, 16, 32, 64, 128) in the upper left and lower left panels,(6, 8, 16, 32, 64, 128) in the upper right panel,and at (4, 8, 16, 32, 64, 128) in the lower right panel.

A55, page 46 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

14281404 1331 1251 1426 1049 813 M 31 NN1 1461 1063 1365 M 31 N1 41:50:00 1104 1014 619 41:50:00 1372 1104 December 2006 1550 1067 1067 808 January 2002 861 757 703 665 1532 1482 1044 986 905 13071286 1044 660 15121500 1113 967 1560 1113 1094 891 702 1589 1143 1094 1143 850 794 765 575 1249 988 898 1489 1440 1401 1294 988 1126 1080 524 1369 1126 1080 45:00 1523 45:00 580 517 1349 699 626 1603 1192 1624 1566 1324 1192 731711 652 561 487 1626 1278 1166 991 958 724 1518 1460 1281 1166 991 958 980 867 980 914 630 784 496 1277 471 1466 1244 1360 1182 1182 1127 931 691 672 1562 1127 93 695 609 1358 637 585 1611 1362 1185 1090 1635 1185 1090 40:00 40:00 1441 1379 1271 1156 11561123 849 1536 1347 1302 1123 751 657 556 502 718 635614 15981590 1498 536 1400 1338 1273 1097 832 664 11211097 950 11331121 950 708 1296 1265 1133 9 197 918 627 550 12201197 641 481 1449 1230 1042 1042 860 43 1599 1520 1248 894 1436 123912281217 1507 1451 1309 1135 900 616 1392 1135 577 15471546 1098 854 1315 1175 1098 117535:00 755 694 492 35:00 1494 1433 1344 1282 1081 489 1390 1081 882 760752 1386 1263 713 438 13041287 947 729 504 1634 1587 1336 1232 947 874 499 1631 1147 712 14461430 1147 530 444 1612 1495 1399 1371 1213 3 719 1057 839 1415 1057 700 564 1420 1348 1205 1158 05 1158 678 1452 1272 1141 1141 1109 818 697 527 494 1109 821 636 10991068 10991068 786 856 824 15351522 1406 1142 30:001142 917 621 403 30:00 1289 970 651 449 1293 989970 1020989 1389 10201007 1007 722 656 407 1616 1357 774 647 1305 1154 1021 461 1537 1297 1154 1021 1567 1275 915 864857 1055 1055 706 1421 1201 1077 505 10771066 1066 896 558 1497 1035 1604 14811473 1173 1035 759 541 1323 1018 739 617 447 1581 1177 467 25:00 1316 1138 1040 25:00 1040 884 1559 0.2 - 4.5 keV 939 574 543 1153 803 775 717 650 591 0.2 - 4.5 keV 1468 929 868 753 1553 1525 1450 1132 1043 661 XMM-Newton 976 539 1416 1340 1212 942 862 602 XMM-Newton 1517 1463 12561236 936 677 618 1373 1319 1191 733 698 671 570 545 EPIC PN + MOS 907 804 766 1332 0:43:00 30838 42:00 30 41:00 40:30 EPIC PN45:00 + MOS 301388 44:00 301194 0:43:00 924 859 688 639 1488 1410 1537 631 1567 1421 1821 1560 1642 December 2006 1791 1637 1589 M 31 NS2 1604 1497 1473 1649 1481 1323 1732 1666 1581 1628 January 2007 1784 1523 25:00 1682 1652 1316M 31 NS1 45:00 1832 1559 1603 1607 1468 1806 1772 1747 1685 1624 1566 1610 1553 1525 1626 1450 1518 1416 1340 1212 1460 1707 1517 1463 12561236 1373 1319 1191 1783 1742 1594 1563 1332 1687 1640 1466 1388 1194 1410 1562 1665 1488 1761 1692 1611 1619 1545 1224 20:00 1694 40:00 1851 1804 1635 1441 750 1234 1180 1660 1536 11116 1675 15981590 1498 12031195 1729 1713 1361 1216 1846 1708 1538 1327 1773 1172 1449 15741554 1472 1723 1325 1643 1599 1520 1681 1580 1788 1436 1469 1717 1507 1451 1457 1721 1734 15961591 1267 11 15471546 1606 1565 1458 1736 1705 1257 1494 1433 15:00 1552 35:00 1731 1508 1351 1261 1214 1730 1661 1669 1199 1634 1587 1540 1367 1291 1623 1703 1631 1430 1328 1298 1807 1766 1612 1446 1502 17331727 1495 1715 1683 1176 1834 1588 1423 1189 1776 1725 1412 1443 1253 1452 1471 1285 1844 1743 1543 1479 1299 1709 1636 1651 1385 1836 1748 8 1447 1240 1825 15351522 1 10:00 1492 41:30:00 1558 1439 1841 1740 1521 1266 1813 1699 1363 12381226 1678 1616 1542 1432 1171 1781 1722 1537 1677 1524 1484 1303 1567 1575 1376 1342 12521231 1816 142 1333 1210 1737 1695 1642 1476 1726 1604 149714811473 1638 1605 1438 1233 1581 1769 1697 41:05:00 1506 1366 25:00 1682 1652 1613 1564 1422 1288 1183 1559 1448 18721863 1792 1431 12501242 1607 1468 1456 1610 1553 1525 1450 1644 1868 17551739 1571 1260 1707 1517 1463 1556 1301 1789 1459 1594 1563 1561 1454 1346 1276 1640 1329 1284 1687 1592 1531 1488 0.2 - 4.5 keV 0.2 - 4.5 keV 1665 1619 1555 1483 1822 1759 1545 00:00 1374 1341 20:00 1694 XMM-Newton XMM-Newton 1786 1750 1713 1490 EPIC PN + MOS 1708 1538 EPIC PN + MOS 1394 1800 1574 14241396 1554 46:00 30 0:45:00 30 44:00 43:30 0:47:00 30 46:001681 301580 45:00 44:30 1455 Fig. A.1. continued. Contours are at (4, 8, 16, 32, 64, 128) in all panels.

A55, page 47 of 51 A&A 534, A55 (2011)

1749 1712 152815151496 1712 152815151496 1654 1749 1654 1754 1688 1633 1485 1754 1688 1633 1485M 31 N2 1763 1728 15011486 M 31 N2 1763 1728 15011486 1516 1516 January 2002 42:10:00 1614 January1453 2007 42:10:00 1614 1453 1751 1689 1411 1751 1689 1762 1403 1762 14111403 18101805 16841676 1656 1621 18101805 16841676 1656 1621 1578 1470 1578 1470 1513 1513 14251419 14251419 1579 1579 1753 1753 1608 1387 1608 1387 1818 1504 1409 1818 1409 1795 1724 1670 1487 1795 1724 1670 15041487 05:00 1704 1570 05:00 1704 1570 1429 1429 1738 1706 1655 1577 1405 1738 1655 1577 1405 1718 1582 17181706 1582 1696 1585 1696 1585 1615 1 1615 1 1663 1391 1663 1391 1803 1646 1597 1803 1646 1597 1780 1657 1780 1657 1629 1601 1629 1601 1667 1593 1667 1593 1632 1442 1343 1632 1442 1343 1833 1720 1551 1833 1720 1551 00:00 1794 1760 1690 00:00 1794 1760 1690 1702 1600 1573 1702 1573 1586 1529 1414 1370 16001586 1529 1414 1370 1530 1467 1354 1467 1653 1530 1354 1828 1710 1548 1408 1828 1653 1548 1408 1630 1359 1710 1630 1359 1671 1671 1659 1569 1509 1382 1659 1569 1382 1793 1622 1793 1509 1799 13 1799 1622 13 1650 1617 1572 1474 1650 1572 1474 1539 1617 1539 1830 1802 1698 1462 13931375 1802 1698 1462 13931375 1771 1527 1830 1771 1527 55:00 1583 55:00 1583 16451625 1549 1505 1645 1549 1505 1768 1768 1625 1337 1337 1765 1534 1765 1534 1673 1673 1711 1672 1378 1711 1378 1744 1620 1541 1514 1672 1620 1541 1514 1809 1664 1533 1428 133 1809 1744 1533 1428 133 1641 1404 1664 1404 1812 1641 1767 1693 1602 1426 1812 1767 1602 1426 1835 1639 1835 1693 1639 1801 1801 1785 1741 1691 1461 1785 1741 1691 1461 1365 1365 41:50:00 1372 41:50:00 1372 1716 1647 1550 1716 1647 1550 1532 1482 1532 1482 15121500 15121500 1821 1560 1821 1560 1791 1637 1589 1791 1637 1589 1649 1649 1732 1489 1440 1401 1732 1489 1440 1401 1666 1666 1784 1628 1784 1628 45:00 1523 45:00 1523 0.2 - 4.5 keV 1603 0.2 - 4.5 keV 1603 1772 1747 1685 1624 1566 1772 1747 1685 1624 1566 1626 1626 XMM-Newton 1518 1460 XMM-Newton 1518 1460 1742 1742 EPIC PN + MOS EPIC30 PN + MOS 46:00 30 0:45:00 30 44:00 30 46:00 30 45:00 30 0:44:00 1562 1562 1692 1611 1235 1268 25:00 42:10:00 1680 14111403 M 31 NN2 M 31 NN3

1065 January 2007 1417 January 2007 14251419 1264 977 1295 1662 1595 1119 1627 1576 1387 1679 1480 1409 1247 1465 1330 42:20:00 05:00 890 1429 1477 1405 1658 1314 987 920 1313 1609 1204 1418 1300 1391 11981179 1437 1274 1510 978962 1757 1584 1499 1270 1128 1004 1343 1442 1686 1161 996 963 1519 1413 945 865 827 15:00 1434 1339 00:00 11931184 1038 1568 1308 1186 1029999 1478 1414 1370 1306 1714 16681648 953 1467 1354 1225 1125 1019 1427 919 812 1528 1408 1359 1255 1749 1712 15151496 1754 16541633 1485 1380 1243 1382 1728 1688 927 1763 15011486 1235 1320 1159 806 1516 1474 1268 1453 1462 13931375 10:001751 1614 55:00 106210391002 749 1762 1689 14111403 5 12221215 848 16841676 1656 1621 1283 1227 983 1337 1223 1190 845 1578 1470 1513 1378 1200 11681150 14251419 1264 1428 1107 1579 1404 1331 1106 1058 1295 1251 1753 1426 1608 1387 1670 15041487 1409 1247 1461 1049 813 1724 1704 1570 1330 1365 1063 05:00 1429 50:00 1372 1104 1014 1738 1655 1577 1405 17181706 1582 1314 1067 808 1696 1585 861 1615 1313 1204 1482 757 703 1663 1391 13071286 1044 986 905 1646 1597 119 1657 1274 1113 967 1629 1601 1270 1143 1094 891 850 765 1667 1593 1249 794 1632 1442 1343 1401 1294 898 1440 988 1720 1551 1369 1126 1080 00:00 1690 1702 45:00 1600 1573 1349 1586 1529 1414 1370 1306 1324 1192 0.2 - 4.5 keV 1278 0.2 - 4.5 keV 1530 1467 1653 1354 1281 1166 991 958 1548 1408 1359 980 914 867 1671 1630 XMM-Newton XMM-Newton1659 1569 1509 1382 1277 1622 1320 1244 1650 1360 1182 1127 1617 1572 1539 1474 EPIC PN + MOS 931 1462 13931375 EPIC PN + MOS 1527 30 44:00 30 43:00 30 0:42:00 0:46:00 301583 45:00 30 44:00 43:30 1185 1090 1625 1549 1505 1302 1271 11561123 Fig. A.1. continued. Contours are at (4, 8, 16, 32, 64, 128) in all panels.

A55, page 48 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31

1852 10:00 1921 1848 1751 1689 1843 1762 18101805 16841676 1756 M 31 N3 M 31 NS3 30:00 1883 1752 June 2002 1916 January 2007 1849 1858 1753 1913 1719 1881 1818 1670 1888 1795 1724 1704 1745 05:00 1847 1775 1738 1853 1829 1942 1901 1706 1655 1718 1696 1798 1735 1862 1870 1701 1908 1663 1615 42:25:00 1895 1803 1646 1597 1817 1680 1941 1919 1780 1657 1904 1629 1601 1875 1667 1939 1902 1632 159 1924 18891873 1782 1764 1935 19141912 1866 1819 179017781770 1894 1833 1720 1922 42:00:00 1794 1760 1690 1906 1864 1837 1702 1936 1746 1662 1595 160105 1854 1826 1627 1576 1905 18791865 1947 1679 20:00 1926 1860 1653 1899 1877 1845 1869 1828 1710 1630 1893 1903 16711659 1815 1658 1793 1799 1622 1857 1609 1650 1617 1937 1884 1898 1830 1802 1771 1698 1900 1823 55:00 1909 1876 1777 1757 1584 1645 1948 1625 1907 1855 1927 1768 1929 1911 1867 1765 1945 1779 1686 1882 1673 1923 1711 1672 1620 15:00 1928 1890 1811 1918 1744 1838 1809 1664 1874 1641 1856 1648 1812 1767 1602 1943 1714 1668 1920 1693 1639 1910 1835 1801 1933 1741 19461938 1932 1859 1785 1691 1944 1749 1712 1654 50:00 1754 1688 1633 19251917 1647 1861 1763 1728 1931 1891 1871 1716 1940 1896 1839 1840 1787 1852 1797 10:00 1751 1614 1892 1934 1921 1848 1689 1762 1684 1821 18101805 1676 1656 1621 1791 1637 1649 1883 1732 1666 1885 1784 1628 1916 41:45:00 1832 1858 1753 1624 1806 1772 1747 1685 1881 1818 1670 1626 1795 1724 1704 05:00 1847 0.2 - 4.5 keV 0.2 - 4.5 keV 1742 1901 1738 1706 1655 1783 1718 1696 XMM-Newton 1908 1862 XMM-Newton 1803 1761 1692 1919 EPIC PN + MOS 1904 1780 40:00EPIC PN + MOS 1851 1804 30 0:47:00 30 46:00 45:30 48:00 30 0:47:00 30 46:00 45:30 1729 1773 1723 1141 1109 818 697 1643 1099 1068 821 1788 856 824 786 1717 30:00 1142 917 M 31 RX 1289 1721 1293 989970 651 M 31 H4 1020 1007 1736 1705 774 722 656 35:00 1305 647 1731 1021 1661 February 2003 1297 1154 1730 1275 857 1055 915 864 1634 1587 1201 706 1807 1703 1631 10771066 896 1766 1727 1612 July 2004 1733 1173 1035 1834 1725 1323 759 1776 1177 1018 739 617 1138 25:001316 1040 1844 1743 884 1709 1153 939 803 591 1636 775 717 650 1836 1748 1522 929 868 753 1535 1132 30:00 1825 1043 661 976 1841 1340 1212 1813 1740 1699 862 602 1256 1236 1092 942 1678 1616 936 677 618 1319 1191 1118 1022 698 671 570 1722 1537 984 733 1781 1332 1115 1076 907 804 766 1567 838 1194 1137 952 924 859 573 1816 688 639 1737 1695 1642 923 631 1224 1134 1102 921 895 687 1726 1604 1 41:20:00 1152 1 1180 829 1930 1234 1144 1581 11671160 1136 798 544 1697 1195 836823 1769 1652 1203 807 669662655 25:00 1682 1216 883 594 547 1872 1792 1559 840 795 628 1863 1327 1131 715 16101607 1172 820 1755 1553 1525 1868 1739 1325 1124 870 610 877 783 1517 654 565 1707 810 740 624 1915 1789 1157 623 578 1594 1563 1267 762 738 584 1640 872 720 1687 15:00 1257 879 855 587 559 1887 888 730 1351 1261 876 788 1665 1214 1619 634 1822 1759 1545 1199 1146 816800 596 20:00 1694 1291 1101 835 911 853 670 1786 993 871 732 1750 1328 1298 11141096 10281011 1013 1176 791 1189 1091 10481032 705 1713 1110 1538 1253 819 645 1897 1708 975 797 681 1800 1285 1117 597 15741554 1299 957 910 1880 1681 1580 782 10:00 1240 604 1105 1842 1734 15961591 606 1886 1606 1565 1266 12381226 1051 615 41:15:00 1149 878 750 1878 1552 1171 748 1774 863 723 1820 1508 1303 979 668 1342 1252 935 814 736 599 1231 1045 1850 1669 1540 1333 1623 1210 826 965 1715 1683 1233 696 1588 1053 925912 799 1831 1085 05:00 684 1288 1183 1543 933 685 1796 1651 0.2 - 4.5 keV12501242 1148 10:000.2 - 4.5 keV 1758 793 1824 1558 XMM-Newton1260 1814 XMM-Newton 1087 841 726 1677 1165 EPIC PN + MOS 934 796 1009 1079 EPIC PN + MOS 906 30 47:00 30 46:00 30 0:45:00 301151 0:43:00 30875 42:00 41:30 1095 959 1638 1031 Fig. A.1. continued. Contours are at (4, 8, 16, 32, 64, 128) in both upper panels and the lower left panel,andat(4, 8, 16, 32) in the lower right panel. The inner area of the image shown in the lower right panel is shown in detail in Fig. A.2.

A55, page 49 of 51 A&A 534, A55 (2011)

1057 839 1205 1158 1141 1109 818 1205 1158 1141 1109 818 1099 1068 821 M 31 Centre1 856 824 786 1099 1068 821 M 31 Centre2 824 786 30:00 1142 917 856 12931289 30:00 1142 917 989970 1289 1020 June 2000 1293 989970 1007 722 1020 December 2000 774 1007 1305 774 722 1154 1021 1305 1297 1154 1021 1275 857 1297 1055 915 864 1275 857 1201 706 1055 915 864 1201 706 10771066 896 10771066 896 1173 1035 1323 759 1173 1035 1323 759 1177 1018 739 617 1138 1177 739 617 1316 1040 1018 25:00 884 1316 1138 41:25:00 1040 884 1153 939 803 775 717 650 1153 939 803 929 753 775 717 650 868 929 1132 1043 868 753 661 1132 976 1043 661 1340 1212 976 942 862 602 1340 1212 1256 1236 1092 936 618 862 602 3 677 1256 1236 1092 942 1319 1191 1118 1022 733 698 671 1373 936 677 618 984 1319 1191 1118 1022 733 698 671 1332 1115 1076 907 804 766 984 838 1332 1115 1076 907 804 766 1194 1137 838 952 924 859 639 573 1194 1137 688 1388 952 924 859 639 923 631 0 688 923 631 41:20:00 1224 1134 1102 921 895 687 1152 1224 1134 1102 921 895 687 1180 20:00 1152 1234 829 1144 1180 829 11671160 1136 798 1234 1144 12031195 836823 11671160 1136 798 807 669662655 1195 836823 1216 883 594 1203 807 669662655 361 840 795 628 1216 883 594 1327 1131 715 1361 840 795 1172 820 1131 628 1327 1172 820 715 1325 1124 870 610 1325 1124 870 610 877 783 740 654 565 877 810 624 783 654 1157 623 578 810 740 624 1267 762 738 584 1157 623 872 720 1267 762 738 5 15:00 1257 879 855 587 872 720 559 15:00 1257 879 855 5 1351 888876 788 730 1261 888 730 1214 1351 1261 876 788 1199 634 596 1214 1146 1101 816800 634 596 367 1291 835 1199 1146 816800 993 911 871 853 670 1291 1101 835 732 1367 853 670 1328 1298 11141096 10281011 993 911 871 732 1328 1298 1114 1013 791 1096 10281011 1176 1013 791 1189 1091 10481032 705 1176 1110 819 1189 1091 10481032 705 1253 975 681 645 1110 819 797 597 1253 681 645 1285 1117 975 797 597 1299 957 910 1285 1117 1299 957 910 782 1385 10:00 1240 604 782 604 1105 10:00 1240 606 1105 1266 606 363 615 12381226 1051 1363 1266 1149 878 750 12381226 1051 615 1171 863 748 1149 878 750 979 723 1171 748 1303 1252 668 863 723 1342 1231 935 814 736 1303 979 668 1045 1342 1252 1231 935 814 736 1333 1045 1210 826 1333 1210 826 965 1233 696 965 1053 1233 696 925912 799 1053 1085 925912 799 05:00 684 1085 1288 1183 05:00 684 933 685 1183 1288 685 0.2 - 4.5 keV12501242 1148 933 793 0.2 - 4.5 keV 12501242 1148 793 1260 XMM-Newton XMM-Newton1260 1087 841 726 1087 841 726 1165 EPIC PN + MOS 934 796 1165 1009 EPIC PN + MOS 934 796 44:00 30 0:43:001079 30 42:00 41:30 44:00 30 0:43:001009 30 42:00 41:30 906 1079 1206 1151 875 906 875 1095 1057 839 1206 1151 839 1205 1158 1057 1141 1109 818 1205 1158 1141 1109 818 1099 1068 821 M 31 Centre3 856 824 786 1099 1068 821 M 31 Centre4 824 786 30:00 1142 917 856 12931289 30:00 1142 917 989970 1289 1020 June 2001 1293 989970 January 2002 1007 722 1020 774 1007 1305 774 722 1154 1021 1305 1297 1021 1275 1297 1154 915 864857 1055 1275 857 1201 706 1055 915 864 1201 706 10771066 896 10771066 896 1173 1035 1323 759 1173 1035 1323 1177 1018 739 617 759 1138 1177 739 617 1316 1040 1018 25:00 884 1316 1138 41:25:00 1040 884 1153 939 803 775 717 650 1153 939 803 929 868 753 775 717 650 1132 929 753 1043 661 868 976 1132 1043 1340 1212 661 862 976 1236 942 602 1340 1212 1256 1092 936 618 942 862 602 1118 677 1256 1236 1092 1319 1191 1022 733 698 671 1373 936 677 618 984 1319 1191 1118 1022 733 698 671 1332 1115 1076 907 804 766 984 838 1332 1115 1076 907 804 766 1194 1137 838 952 924 859 639 573 1194 1137 688 1388 924 631 10 952 859 639 923 688 631 41:20:00 1224 1134 1102 921 895 687 923 1152 1224 1134 1102 921 895 687 1180 20:00 1152 1234 829 1144 1180 829 11671160 1136 798 1234 1144 12031195 836823 11671160 1136 798 807 669662655 836823 12031195 655 1216 883 840 795 594 807 669662 1 628 1216 883 594 1327 1131 715 1361 840 795 1172 820 1131 628 1327 1172 820 715 1325 1124 870 610 1325 610 877 1124 870 783 654 740 624 565 877 783 810 623 578 740 654 1267 1157 810 624 762 738 584 1157 623 872 720 1267 762 738 15:00 1257 879 855 587 872 720 559 15:00 1257 879 855 1351 888876 788 730 1261 888 730 1214 1351 1261 876 788 634 596 1214 1199 1146 1101 816800 634 1291 835 1199 1146 816800 596 993 911 871 853 670 1291 1101 835 1328 1298 732 1367 911 853 670 11141096 10281011 993 871 732 1328 1298 1114 1013 791 1096 10281011 1176 1013 791 1189 1091 10481032 705 1176 1110 819 1189 1091 10481032 705 1253 681 645 1110 975 797 597 1253 819 645 1285 1117 975 797 681 1299 957 910 1285 1117 597 1299 957 910 782 1385 10:00 1240 604 782 1105 10:00 1240 604 606 1105 1266 606 3 1226 615 1238 1051 1363 1266 1149 878 750 12381226 1051 615 1171 863 748 1149 878 750 979 723 1171 748 1303 1252 736 668 863 723 1342 1231 935 814 1303 979 668 1045 1342 1252 1231 935 814 736 1333 1045 1210 826 1333 1210 826 965 1233 696 965 1053 1233 696 925912 799 1053 1085 925912 799 05:00 684 1085 1288 1183 05:00 684 933 685 1183 0.2 - 4.5 keV 1288 685 12501242 1148 0.2 - 4.5 keV 933 793 12501242 1148 793 1260 XMM-Newton XMM-Newton1260 1087 841 726 1087 841 726 EPIC PN + MOS 1165 934 796 EPIC PN + MOS 1165 1009 934 796 30 0:43:001079 30 42:00 41:30 0:44:00 30 43:001009 30 42:00 41:30 906 1079 1206 1151 875 906 875 Fig. A.1. continued. Contours are at (6, 8, 16, 32) in both upper panels,at(8, 16, 32) in the lower left panel,andat(4, 8, 16, 32) in the lower right panel. The inner area is shown in detail in Fig. A.2.

A55, page 50 of 51 H. Stiele et al.: The deep XMM-Newton Survey of M 31 122 944 122 944 1006 1006 1012 C1 1012 C2 1017 8 1017 8 1 1 1059 1059 1100 985 1100 985 104610241005 104610241005 10231015 940 922 10231015 940 922 124 1103 1075 1010990 966 124 1103 1075 1010990 966 1034 994 1034 994 997 971 997 971 1061 1033 1061 1033 1116 1093 1036 981 1116 1093 1036 981

992 992 968 968 10251016 10251016 1108 960 1108 960 88 88 974 974 1000 930 1000 930 1056 1056 1101 1101 993 911 993 911 122 944 122 944 1006 1006 1012 C3 1012 C4 1017 8 1017 8 1 1 1059 1059 1100 985 1100 985 104610241005 104610241005 10231015 940 922 10231015 940 922 124 1103 1075 1010990 966 124 1103 1075 1010990 966 1034 994 1034 994 997 971 997 971 1061 1033 1061 1033 1116 1093 1036 981 1116 1093 1036 981

992 992 968 968 10251016 10251016 1108 960 1108 960 88 88 974 974 1000 930 1000 930 1056 1056 1101 1101 993 911 993 911 122 944 1006 1012 RX 1017 8 1 1059 1100 985 104610241005 10231015 940 922 124 1103 1075 1010990 966 1034 994 997 971 1061 1033 1116 1093 1036 981

992 968 10251016 1108 960 88 974 1000 930 1056 1101 993 911 Fig. A.2. Inner area of M 31 enlarged from Fig. A.1. Contours are at (4, 8, 16, 32, 64, 128, 256) × 10−6 ct s−1 pix−1 including a factor of one smoothing. Sources from the large catalogue are marked as 30 × 30 squares. The images are ordered as follows: Centre 1 (upper left), Centre 2 (upper right), Centre 3 (middle left), Centre 4 (middle right) and Centre B (lower left).

A55, page 51 of 51

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