A&A 457, 1081–1093 (2006) Astronomy DOI: 10.1051/0004-6361:20065062 & c ESO 2006 Astrophysics
A catalogue of Galactic supernova remnants from the Canadian Galactic plane survey I. Flux densities, spectra, and polarization characteristics
R. Kothes1,2, K. Fedotov1,3, T. J. Foster1, and B. Uyanıker4,1
1 National Research Council of Canada, Herzberg Institute of Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia, V2A 6J9, Canada e-mail: [email protected] 2 Department of Physics and Astronomy, University of Calgary, 2500 University Drive N.W., Calgary, AB, Canada 3 Department of Physics and Astronomy, University of Victoria, PO Box 3055, STN CSC, Victoria, BC, V8W 1A1, Canada 4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany Received 21 February 2006 / Accepted 23 May 2006 ABSTRACT
We present a new catalogue containing all known Galactic supernova remnants observed in phase I and II of the Canadian Galactic Plane Survey (65◦ ≤ ≤ 175◦, −5◦ ≤ b ≤ +7◦). Stokes I images at 1420 MHz of 34 SNRs and at 408 MHz of 36 SNRs are displayed. From these 1 and 3-resolution data (respectively) we determine accurate centre positions and angular dimensions. The flux densities at 1420 and 408 MHz are integrated and combined with values from the literature to define more accurate radio spectra. The CGPS polarization data at 1420 MHz were examined and significant linear polarization from 18 SNRs is found, with a modest signal from 6 others. Key words. atlases – catalogs – polarization – ISM: supernova remnants
1. Introduction now becoming available in the Canadian Galactic Plane Survey (CGPS, Taylor et al. 2003). The CGPS data probe the ion- As the most significant source of chemical enrichment, energy ized, neutral, particulate, and magneto-ionic media over un- input, and cosmic ray production in the interstellar medium precedented spatial dynamic range, and are allowing new in- (ISM), supernovae play an important role in the evolution of sights into the SNR population in our Galaxy. The synthesis our Galaxy. According to a simple calculation by Padmanabhan telescope at the Dominion Radio Astrophysical Observatory (2001) about 55% of the material in the Milky Way would (DRAO, Landecker et al. 2000) has been used to undertake si- have been processed by supernova explosions and their rem- multaneous observations at two radio frequencies providing data nants. Detailed understanding of the properties of Galactic su- for Stokes I at 408 MHz and full linear polarization information pernova remnants (SNRs) – sizes, energies, statistics, etc. – is at 1420 MHz. This spectacular dataset has already been used to thus of great importance in understanding the physical struc- discover five low surface brightness SNRs (Kothes et al. 2001; ture of the interstellar medium (ISM). Ultimately, such under- Kothes 2003; Kothes et al. 2005). standing rests on estimation of accurate unbiased characteristics In this, the first part of the CGPS SNR catalogue, we of SNRs. However, characteristics of identified SNRs are often present images, newly determined flux densities at 408 MHz poorly known (for example, spectral and polarization proper- and 1420 MHz in Stokes I, and fractional linear polarization ties and even total angular extent), and in particular distances to at 1420 MHz, for a total of 36 supernova remnants in the first these objects are quite ill-defined. A problem significant at low and second quadrants of the Milky Way. We also include all flux radio frequencies and low resolution is the contribution of galac- / densities we could find published in the literature to determine tic extragalactic point sources to the total flux, which results in more accurate radio spectra for these SNRs. overestimated flux values. Additionally the total dimension of In the second part of the catalogue (in prep.) distances, di- a given SNR may not be easily found due to diffuse extended mensions, and the spatial distribution of the SNR population will emission that cannot be detected by telescopes with low sensi- be discussed. A planned third part will contain a statistical anal- tivity or interferometers due to missing single antenna data. This ysis of the newly determined SNR properties. would lead to an underestimate of the real fluxes. These effects contribute to conflicting flux density measurements for the same source at similar frequencies, which are indeed very often found throughout the literature. 2. Observations and data processing Unbiased, high resolution, wide-field images of all ma- 2.1. Observations jor constituents of the Galactic ISM in the Outer Galaxy are The radio continuum data were obtained using the synthesis tele- Figures 2–6 and 8–10 are only available in electronic form at scope (ST) of the Dominion Radio Astrophysical Observatory http://www.edpsciences.org (DRAO, Landecker et al. 2000) as part of the Canadian Galactic
Article published by EDP Sciences and available at http://www.edpsciences.org/aa or http://dx.doi.org/10.1051/0004-6361:20065062 1082 R. Kothes et al.: SNR catalogue. I.
Table 1. Newly determined centre positions and angular dimensions Θmaj and Θmin of all 36 Galactic supernova remnants that can be found in the area observed for the CGPS. Equatorial coordinates (J2000) are given in [hh mm ss] for Right Ascension and in [+dd mm] for Declination. The dimensions were determined from the radio emission as seen at 1420 MHz except for DA 530 and G156.2+5.7 (marked with ∗), which are only covered by the 408 MHz survey. The designations of 1420 and 408 MHz CGPS mosaics are given in the last column (see text).
◦ ◦ ◦ ◦ Source [ ] b [ ]RAJ2000 DecJ2000 Θmaj [ ] Θmin [ ] Mosaic Codes G65.1+0.6 65.14 +0.41 19 53 57 +28 32 1.17 1.13 MR1 + C7 G65.7+1.2 65.72 +1.20 19 52 13 +29 26 0.38 0.35 MR1 + C7 G67.7+1.8 67.74 +1.80 19 54 38 +31 28 0.25 0.20 MQ2 + C7 G68.6−1.2 68.59 −1.21 20 08 40 +30 36 0.38 0.38 MQ1 + C7 G69.0+2.7 68.81 +2.57 19 54 07 +32 47 1.88 1.48 MQ2 + C7 G69.7+1.0 69.69 +1.01 20 02 38 +32 43 0.27 0.23 MQ2 + C7 G73.9+0.9 73.83 +0.90 20 13 57 +36 08 0.47 0.43 MP2 + C6 G74.9+1.2 74.96 +1.15 20 16 03 +37 13 0.17 0.13 MP2 + C6 G76.9+1.0 76.89 +0.97 20 22 20 +38 43 0.15 0.13 MO2 + C6 G78.2+2.1 78.18 +2.12 20 21 14 +40 26 1.13 1.13 MO2 + C6 G82.2+5.3 82.17 +5.29 20 19 11 +45 30 2.05 1.47 MN2 + C6 G83.0−0.3 83.02 −0.27 20 46 54 +42 52 0.15 0.12 MM1 + C6 G84.2−0.8 84.20 −0.81 20 53 22 +43 27 0.40 0.32 MM1 + C6 G84.9+0.5 84.99 +0.50 20 50 33 +44 54 0.13 0.13 MM1 + C6 G85.4+0.7 85.38 +0.73 20 50 57 +45 21 0.70 0.65 MM1 + C6 G85.9−0.6 85.96 −0.63 20 58 58 +45 44 0.50 0.50 MM1 + C6 G89.0+4.7 89.05 +4.67 21 27 31 +57 20 2.50 2.27 ML2 + C5 G93.3+6.9∗ 93.26 +6.91 20 52 19 +55 20 0.48 0.43 C5 G93.7−0.2 93.75 −0.36 21 29 56 +50 44 2.00 1.73 MK1 + C5 G94.0+1.0 94.00 +1.03 21 24 56 +51 54 0.63 0.55 MK1 + C5 G96.0+2.0 96.06 +1.96 21 30 33 +54 00 0.45 0.43 MIJ2 + C5 G106.3+2.7 106.35 +2.79 22 27 40 +60 57 1.07 0.70 MG2 + C4 G107.5−1.5 107.26 −1.68 22 50 51 +57 29 0.16 0.14 MF1 + C4 G109.1−1.0 109.15 −1.02 23 01 39 +58 53 0.58 0.52 MF1 + C4 G113.0+0.1 112.98 +0.13 23 26 54 +61 21 0.76 0.60 ME1 + C3 G114.3+0.3 114.32 +0.34 23 37 08 +61 58 1.48 1.27 ME1 + C3 G116.5+1.1 116.43 +1.10 23 53 12 +63 14 1.32 1.22 MD2 + C3 G116.9+0.2 116.94 +0.19 23 59 16 +62 27 0.62 0.62 MD1 + C3 G120.1+1.4 120.09 +1.41 00 25 20 +64 08 0.18 0.18 MC2 + C3 G126.2+1.6 126.23 +1.76 01 22 04 +64 26 1.48 1.42 MB2 + C2 G127.1+0.5 127.11 +0.56 01 28 33 +63 08 0.98 0.88 MA1 + C2 G130.7+3.1 130.73 +3.08 02 05 43 +64 49 0.18 0.10 MA2 + C2 G132.7+1.3 132.65 +1.56 02 18 03 +62 47 2.07 1.78 MY2 + C2 G156.2+5.7∗ 156.17 +5.61 04 58 37 +51 45 1.82 1.59 C0 G160.9+2.6 160.38 +2.74 05 00 35 +46 41 2.48 2.32 MEY2 + C0 G166.0+4.3 166.14 +4.25 05 26 27 +42 54 1.60 0.83 MEX2 + CM1
Plane Survey (Taylor et al. 2003). Single antenna data are incor- The CGPS data are released in the form of 5◦ × 5◦ mo- porated into the Stokes I synthesis maps to ensure accurate rep- saics (called “M” mosaics), at all frequencies. The larger primary resentation of all structures from the largest scales down to the beam at 408 MHz provides a much larger sky coverage; hence resolution limit. The short spacing data and the DRAO ST obser- at this frequency 15◦ × 15◦ mosaics (“C” mosaics) are created vations are merged in Fourier space using a normalized tapering in addition to the M-mosaics. The CGPS is available to the com- function in the overlap region. The low spatial frequency contin- munity through the Canadian Astronomy Data Centre (CADC 1). uum data for the 408 MHz observations were derived from the To make it easier to find each SNR in the CGPS data base we list Haslam All-Sky survey (Haslam et al. 1982). For the 1420 MHz the designation code of the mosaics in which each SNR can be Stokes I data, the 1.4 GHz Effelsberg survey (Reich et al. 1997) found in Table 1. At the time of writing the low longitude mo- is used to augment the DRAO interferometer data. Where these saics ( <75◦) are not yet available at 408 MHz. They will be data are not available, the missing spatial frequencies are derived released before the end of May, 2006. from the 1.4 GHz Stockert 25 m Northern Sky Survey (Reich 1982; Reich & Reich 1986). 2.2. The SNR sample Low spatial frequency data for our linear polarization ob- Our sample of Galactic SNRs is mainly based on Green’s servations at 1420 MHz are currently not available. The low Catalogue of Galactic Supernova Remnants (Green 2004). We spatial frequency limit is determined by our shortest antenna discuss all SNRs that are covered by phase I and phase II of the spacing, about 13 m. This corresponds to angular dimensions CGPS (65◦ ≤ ≤ 175◦ and −5◦ ≤ b ≤ +7◦). This includes ◦ × ◦ δ δ of about 1 1 cosec ( )(: Declination of the observation). 35 Galactic supernova remnants and 11 possible SNRs. Hence, for SNRs larger than this in angular size we miss some Three of the 35 SNRs are excluded from the catalogue. ff of the di use polarized emission. The angular resolution of the Cas A is excluded from CGPS observations for reasons of final I, Q, and U data products varies slightly across the maps dynamic range, as discussed in Taylor et al. (2003). The as 0.82 × 0.82 cosec (δ) and 2.8 × 2.8 cosec (δ) at 1420 MHz and 408 MHz, respectively. 1 http://cadc-ccda.hia-iha.nrc-cnrc.gc.ca/cgps R. Kothes et al.: SNR catalogue. I. 1083 observations containing Cas A are exceptionally difficult to cal- integrated by defining a polygon around the emission region. A ibrate due to the extreme brightness of this SNR. It is included twisted plane is fitted to this polygon’s perimeter to determine in Green’s catalogues of Galactic supernova remnants (Green the background contribution, which is then subtracted. The final 2004), but its emission properties will not be discussed further flux density of each supernova remnant is tabulated in Table 3. in this work. We will, however, include Cas A in the forth- This procedure was double checked by estimating a constant coming papers based on this SNR catalogue, which will focus background from the area around the SNR. The errors in the on distances and SNR statistics. The “Galactic SNR” OA 184 listed flux densities consist mainly of the background uncer- (G166.2+2.5) has rather conclusively been shown by Foster et al. tainty, with a contribution from a calibration error (3% and 6% (2006) to be a misidentified H region, as it lacks polarized at 1420 MHz and 408 MHz, respectively). The background un- emission and shines in recombination lines H103-110α, both ob- certainty can be very high in areas of varying background emis- served at λ6 cm. It is hereafter to be excluded from this and fu- sion like the Cygnus X region or for very faint supernova rem- ture catalogues of SNRs. G65.3+5.7 is a rather faint high latitude nants where the fluctuations of the source are comparable to object which is covered by CGPS 408 MHz measurements, but those in the background. due to its low surface brightness and the high noise in its vicinity, Since we merge the data observed with the DRAO ST to- we were not able to detect this source in our data. gether with the low spatial frequency observations in Fourier Additionally we investigated the nature of the 11 “possi- space it is usefull to estimate the percentage of the SNR flux ble” SNRs listed in Green (2004). For the following seven, re- density that is actually derived from the new DRAO ST sults were inconclusive. G71.6−0.5, G72.2−0.3, and G85.2−1.2 observations. At 408 MHz the uv-data is merged using (Taylor et al. 1992) are confused with background emission to a normalized tapering function between spatial dimensions an extent that a distinct flux density measurement is difficult. of 1◦.7(×1◦.7 cosec (δ)) and 3◦.4(×3◦.4 cosec (δ)). Hence for at G75.5+2.4 is suggested to be an SNR by Nichols-Bohlin & least 29 SNRs out of our sample the flux density is entirely based Fesen (1993) and is quite visible in the 1420 MHz data, but is on the new DRAO ST observations. For HB 9, the largest SNR missing in our 408 MHz measurements. This could be caused in our sample (2◦.5 × 2◦.3), the contribution to the flux from the by a flat, thermal radio spectrum and/or confusion with arti- Haslam survey data is less than 30%. At 1420 MHz we apply facts from nearby Cygnus A. At the positions of the candidates the normalized tapering function between 0.◦5(×0◦.5 cosec (δ)) G69.4+1.2 (Yoshita et al. 1999), G117.7+0.6 (Hailey & Craig and 1◦.5(×1◦.5 cosec (δ)) for the Effelsberg survey and between 1995) and a possible remnant at = 70◦ and b =+2◦ (sug- 0◦.75 (×0◦.75 cosec (δ)) and 1◦.5(×1◦.5 cosec (δ)) for the Stockert gested by Mavromatakis et al. 2002) we find no significant radio survey. Hence, for at least 15 SNRs the flux density is en- continuum emission at either 408 or 1420 MHz. tirely derived from the new DRAO ST observation. For HB 9 Two of the 11 possible remnants are clearly thermal in origin. the contribution of the Effelsberg survey is about 70%, for These are the SNR candidates G74.8+0.63 (Zhang 2003) and VRO 42.01.05 (1◦.6 × 0◦.8) this number drops to less than 30%. G104.7+2.8, published by Green & Joncas (1994). They have flat radio spectra between 408 and 1420 MHz and are also very bright infrared sources. 3. Results The following two “possible” SNRs listed in Green’s 3.1. The structure of the SNRs in Stokes I and their spectra catalogue (Green 2004) were added to our SNR catalogue. G83.0−0.3, discovered by Taylor et al. (1992) has a dis- In Figs. 1 and 2–6 we display Stokes I images of all SNRs within tinctly non-thermal radio spectrum and no infrared counter- the bounds of the CGPS at 1420 MHz (65◦ <