PoS(Extremesky 2011)070 poSAX http://pos.sissa.it/ hard state and the / 17 minutes when the ∼ ce. l the data (using XMM-Newton strong gravity and dense matter. ce is in a low ). binary 4U 0513-40 in the globular culty in measuring orbital periods y y y y ◦ orbital nature of the detected signal ffi 80 mpact X-ray binaries and their iden- i s that the accretion onto neutron stars with a period of > ive Commons Attribution-NonCommercial-ShareAlike Licen soft state with a dominant soft thermal component (using Bep / ∗ [email protected]; IASF-Roma, Via Fosso del Cavaliere 100, I-00133, Roma, Ital IASF-Roma, Via Fosso del Cavaliere 100, I-00133, Roma, Ital IASF-Roma, Via Fosso del Cavaliere 100, I-00133, Roma, Ital IASF-Bologna, Via P. Gobetti 101, I-40129 Bologna, Italy IASF-Roma, Via Fosso del Cavaliere 100, I-00133, Roma, Ital / / / / / Speaker. cluster NGC1851 reveals a clear sinusoidal periodic signal in low mass X-ray binaries. The ultracompact low-mass X-ray source is in a typical high tification is very important, albeit complex because of the d and black holes provides a uniqueFor window this on the reason, physics a of renewed the interest has developed in ultraco The principal motivations for studying the X-ray binaries i thermal soft component is no longerand INTEGRAL required observations). any These more properties to indicate mode the and imply an high inclination angle of the binary system ( and Chandra data). The periodicity disappears when the sour ∗ Copyright owned by the author(s) under the terms of the Creat c

M. Fiocchi INAF The 17 min inBinary the 4U Ultra 0513-40 Compact in X-ray the X-ray energy band E-mail: A. Bazzano INAF L. Natalucci INAF R. Landi INAF P. Ubertini INAF The Extreme and Variable High EnergySeptember Sky - 19-23, extremesky2011, 2011 Chia Laguna (Cagliari), Italy PoS(Extremesky 2011)070 5 ∼ orb − P -line Bep- 4 ff (Weis- . M. Fiocchi hard state, τ s in which / ) shorter than . We extracted 1 Chandra orb P he observation files n the EPIC-pn cam- 20 keV and culty to measuring ffi & ectors. Broad-band spectra, Science Data Center (ISDC, h instruments on board CIAO website al periods ( n the canonical low binaries lists 27 candidates (in kTe S cluster, designed to optimize een processed using the O tal period are in the ultracompact esults from long-term monitoring 010). s (Federici et al. 2010). uments, JEM-X (Lund et al. 2003) cmin radius. The PDS spectra were a companion low mass star. UCXBs l Fiume 1997). The -set regions close to the source. ibration Data Base), provided by the with an extraction region of 8 arcsec. r NGC 1851 with a 17-minute orbital (Zurek et al. 2009). It is a persistent ff Interactive Analysis of Observations) the same CCD of the studied source. cular regions of 10 arcsec centered on Guainazzi & Grandi 1999). Both LECS INTEGRAL 10 in X-ray luminosity on timescales of ∼ cult because of the di Chandra . ffi 2 , plasma temperature (Boella et al. 1997) event files and spectra were gener- 1 − INTEGRAL erg s / Hubble 36 ciao BeppoSAX and / / 10 × 7 (Winkler et al. 2003) data consist of all public observation . cxc.harvard.edu // XMM-Newton . X-ray events corresponding to patterns 0-4 were selected i , (Turner et al. 2001) data have been processed starting from t INTEGRAL X-ray Center and following the science threads listed on the Chandra , SAS 7.0.0 Ultracompact X-ray binaries (UCXBs) are systems with orbit Available at http: The LECS, MECS and PDS Table 1 gives a summary of source observations performed wit 1 5–80 keV, are obtained using data from the high-energy instr 1 hr in which a neutron star or black hole accretes matter from in LMXBs. The ’t Zand recent et compilation al., of 2007). Eight ultracompactregime out (in X-ray of ’t 52 Zand LMXBs et with al.of measured 2007, the orbi Nelemans UCXBs & showed Jonker that 2006). these IBIS r sources spend most of the time i Scientific Analysis (OSA v. 9.0) software released by the and IBIS (Ubertini et al. 2003). The IBIS and JEM-X data have b are rare objects and their identification is very di with era. Source light curves andthe spectra source, were while extracted background from products cir wereThe obtained analyzed from o 4U 0513–40 was within the∼ field of view of the IBIS and JEM-X det ≈ Courvoisier et al. 2003).performances and These disk storage runs for were the performed INTEGRAL data with analysi AVE skopf 1999) data were processed with the CIAO ( The 17 min orbital period in 4U 0513-40 1. Introduction with X-ray luminosities software, version 4.1.2, i.e. theChandra same version of CALDB (Cal and MECS spectra were accumulated inextracted circular using regions the of XAS 8 version ar 2.1 package (Chiappetti & Da ated with the Supervised Standard Science Analysis (Fiore, source photons from a circular regionFor centered the on background, the we source used circularXMM-Newton source-free regions in poSAX (Fiocchi et al. 2008). 4U 0513-40 is an X-ray binarymodulation in first the Galactic observed globular with cluste the weeks, and a factor of more than 20 overall (Maccarone et al. 2 2. Observations and Data Analysis source showing evidence for variability of a factor of PoS(Extremesky 2011)070 rgy 18) ± he time data was M. Fiocchi t curve and Chandra X-ray light curves, -5 keV data Phase confidence level. Using this σ mean source count rate). INTEGRAL dure used for 099 Hz is clearly observed. The right panel) with a pulsed fraction Israel & Stella (1996). The power and que. The best-fit period is (1004 pe of the modulation was found (see 0 0.5 1 1.5

MJD ks

. . . 1.2 1.1 1 0.9 0.8 Norm Intens Ser 1 Ser Intens Norm XMM-Newton 3 −3 8×10 in this energy range and calculated a power spectrum EPIC-pn 52730.0 23.5 / σ JEM-XIBIS 53917.6 102.8 53380.4 601.5 ACIS 54560.6 18.8 14) s with uncertainties at 1 / / / LECSMECSPDS 51597.6 51597.6 31.5 51597.6 73.6 34.9 / / / ± light curve in the 3-5 keV energy band, with exclusion of the 140 −3 4%. ∼ ∼ 6×10 data, we accumulated a 16s bin light curve in the 0.3-5 keV ene BeppoSAX BeppoSAX BeppoSAX XMM Newton Instrument TstartCHANDRA Exposure INTEGRAL INTEGRAL observation, a type-I thermonuclear burst was detected at t Summary of the X-ray binary 4U0513-40 observations confidence level. Using this period value, we folded the ligh −3 BeppoSAX / σ 4×10 Chandra Frequency (Hz) / Table 1: The power spectrum and efolding phase diagram using ACIS 0.3 BeppoSAX −3 Figure 1: 11% (i.e. the semi amplitude of the modulation divided by the Using the ACIS During the We have also searched for periodicity in the

0 2×10

04 60 40 20 0 ∼ Power 3. Temporal analysis The 17 min orbital period in 4U 0513-40 s with uncertainties at 1 a sinusoidal shape of theof modulation was found (see Figure 1, band of 4U 0513–40over detected the at whole observation followingspectrum the is method shown outlined in by Figure4U 1 0513–40 period (left was obtained panel) with where an -folding a techni peak at 0.00 burst data. The best-fit period is (1013 applied to 10s bin MECS 51597 MJD - 15:29:55s (see below for details). The same proce but no periodic signals were detected. period value, we folded thefigure light 2) curves with and a a pulsed sinusoidal fraction sha of PoS(Extremesky 2011)070 . 1 − ror ec- s 2 light 7 387 128 284 127 − / / / / / Chan- d.o.f / 2 χ M. Fiocchi INTEGRAL erg cm 1 9 − − s 2 BeppoSAX / − 10 × 15.2 156 Flux erg cm 11 − 10 s) with a simple black- ∼ 10 average spectrum: 5: y burst starting at 51597 MJD een detected, during the 4 0.7 280 3 . . 5 4 18.9 155 71). The absorbed1–10 keV flux are . 3 20 8.9 573 0 . 15 8 − 50 11.0 3 ± 2 ± ± + − 6 < 7 10 . = . COMPTT 0 2 n e extracted the MECS ure time of Chandra χ ∆ burst event was described by Homer et al. 7 5 . . t( 16 38 2 2 + − ± ... 86 ... 8 BB2 9 . n 4 Chandra 6 21 / 6 3 . . . 4 ... 2 3 0 2 3 . 9 1 + − 2 + − τ ± ± 6 2 . 6 8 < . 0.1keV with a extrapolated flux of 3.3 3 ± average spectrum; 4: fixed to the Galactic column density was included in the fit. Er 2 6 . 22 s, computed from exponential fits to the burst decay profile 0 e 2 10 32 16 H . 1: BeppoSAX spectrum before the burst event; 2:BeppoSAX sp 24 2 41 3 ∼ + − + − 1 ± + − + − N kT − τ 6 . s The efolding phase using MECS 3-5 keV data 2 − XMM-Newton 05 5 04 7 02 2 002 15 . . . . 0 0.5 1 1.5 1 21

0 0 0 0 .

erg cm 0 1 1.05 1 0.95 Figure 2: ± ± ± ± T

11 < 13 1 Ser Intens Norm 22 18 − . . . 068 observations. The first HRC . 04 0 04 0 . . 0 0 BB ± ± keV keV keV Spectral analysis results. A kT BeppoSAX 34 49 . . In the soft X-ray band, two thermonuclear X-ray bursts have b and 4 0 3 ... 0 5 ... 1 ... 0 2 0 dra Table 2: The 17 min orbital period in 4U 0513-40 are given at 90% confidence level for one parameter of interes reported in units of 10 trum after the burst event; 3: average spectrum (2001). For the second, not yet reported in the literature, w curve in the 1.5-10 keV(15:29:55 keV s), energy with a band decay and time of we detected an X-ra body model, a thermal temperature of 1.6 Fitting the spectrum (extracted at the burst peak with expos in 0.1-30 keV energy band has been derived. PoS(Extremesky 2011)070 and data, erent ff 17 min COMPTT . Adding ≃ M. Fiocchi H d.o.f. from P / N 2 Chandra χ BeppoSAX , respectively. 4 − 10 esulted in a substantial × re time, 18.8 and 23.5 ks, on, in XSPEC by pectively. For odic signal with 128 for the / and 9 source from each science win- e shown in Figure 3 in di INTEGRAL 13 spectra are shown together with the le and source was detected above − t with the LECS, MECS and PDS 10 ed by a column density, × 130 to 155 / 10 INTEGRAL and 5 (after the burst) data. This reduces channel energy (keV) CHANDRA data and from 173 XMM-Newton BeppoSAX spectra before the burst event with the LECS, MECS and PDS , and Chandra XMM−Newton Chandra , 1 BeppoSAX Chandra BeppoSAX pre−Burst BeppoSAX post−Burst 308 for the

/

observations, to extract the spectra we use the total exposu

BeppoSAX

.10.1 0.01 10 10

−3 −4

keV (keV/cm keV s keV) s 2 The We extracted the The spectral fit results are reported in Table 2 and spectra ar The binary system 4U 0513-40 in NGC 1851 exhibits a clear peri Each spectrum was fitted with a model of thermal Comptonizati 310 to 374 / . The exposure times are 103 ks and 36 ks for IBIS and JEM-X, res σ Figure 3: The 17 min orbital period in 4U 0513-40 4. Spectral behavior of the persistent emission total model and its components. XMM-Newton exposure times of 1.6, 3.4exposure times and of 1.5 30.1, ks, 67.5 and andIBIS 31.2 after and ks, the JEM-X respectively. burst spectra even aredows produced in summing the up period spectra of5 for the which both instrument data are availab colors. 5. Discussion with the low corresponding F-test chance probabilities of 4 (Titarchuk 1994; a spherical geometry was assumed), absorb respectively. 452 a blackbody component (modeledfit in improvement XSPEC for by BBODYRAD model) r PoS(Extremesky 2011)070 0. / hard state M. Fiocchi / BeppoSAX 10 / optical obser- / and 033 / has shown the same 10%. It is observed ∼ cookbook) Chandra / 4% to ∼ AF contract I software / the origin of this modulation is of d luminosity of the system, which from oSAX NFI Spectral Analysis Cookbook , L27 p, data Analysis in Astronomy, 101 g properties seen in UV 9-092 299 (Arons and King 1993). 0605722 ◦ / en when the source is in a low bepposax / after the burst) when the source is in a typical 6 BeppoSAX in the 0.5-50 keV energy band, for and 1 − data). erg s 36 Chandra 10 × INTEGRAL and soft state. This result is independent from the extrapolate for BeppoSAX NFI Spectral Analysis (www.asdc.asi.it The far-ultraviolet photometry obtained with the The authors acknowledge the ASI financial support via ASI-IN / [3] Chiappetti L. & Dal Fiume D.,[4] 1997, in Courvoisier Proc. T. Fifth J.-L. Worksho et al., 2003,[5] A&A 411, L53 Federici M., Martino B. L. and Natalucci L., 2009, PoS200 [1] Arons J. & King I. R.,1993,[2] ApJ, 413, Boella, L121 G.; Butler, R. C.; Perola, G. C. et al., A&AS, 122, [6] Fiocchi M. et al., 2008, A&A,[7] 492, 557 Fiore F., Guainazzi M. & Grandi P. 1999, Cookbook for Bepp [8] Homer L. et al., 2001, ApJ,[9] 550, L155 in ’t Zand J., Jonker P. & Markwardt C., 2007, A&A, 465, 953 XMM-Newton References periodicity described here (Zurek etvations al. and 2009). the These eclipse timin observedorbital in nature the and the X-ray inclination band angle imply is that higher than 80 Acknowledgments (after the burst), respectively. This( periodicity is not se high spans from 0.7 to 5.2 The 17 min orbital period in 4U 0513-40 in soft X-ray. This signal is sinusoidal and has an amplitude [14] Turner M.J.L., Abbey A.F., Arnaud M. et al. 2001, A&A 365 [15] Titarchuk L., 1994, ApJ, 434, 570 [16] Ubertini P. et al., 2003, A&A,[17] 411, L131 Weisskopf M. C., 1999, AAS, 195,[18] 9601 Winkler C. et al., 2003, A&A,[19] 411, 1 Zurek D.R. et al., 2009, ApJ, 699, 1113 [10] Israel G. & Stella L., 1996,[11] ApJ, 468, Lund 369 N., et al. 2003, A&A,[12] 411, L231 Maccarone T. et al. 2010, MNRAS,[13] 406, 2087 Nelemans G. & Jonker P. G., 2006, astro, arXiv:astro-ph only in two observations (