J/ApJS/187/495 SNRs in M33 from optical and X-ray (Long+, 2010)
The Chandra ACIS survey of M33: X-ray, optical, and radio properties of the supernova remnants. Long K.S., Blair W.P., Winkler P.F., Becker R.H., Gaetz T.J., Ghavamian P., Helfand D.J., Hughes J.P., Kirshner R.P., Kuntz K.D., McNeil E.K., Pannuti T.G., Plucinsky P.P., Saul D., Tullmann R., Williams B. <Astrophys. J. Suppl. Ser., 187, 495-559 (2010)> =2010ApJS..187..495L
ADC_Keywords: Galaxies, optical ; X-ray sources ; Supernova remnants ; Morphology Keywords: galaxies: individual (M33) - galaxies: ISM - ISM: supernova remnants - radio continuum: galaxies Abstract: M33 contains a large number of emission nebulae identified as supernova remnants (SNRs) based on the high [SII]:Hα ratios characteristic of shocked gas. Using Chandra data from the ChASeM33 survey with a 0.35-2keV sensitivity of ∼2x1034erg/s, we have detected 82 of 137 SNR candidates, yielding confirmation of (or at least strongly support for) their SNR identifications. A spectral analysis of the seven X-ray brightest SNRs reveals that two, G98-31 and G98-35, have spectra that appear to indicate enrichment by ejecta from core-collapse supernova explosions. We have used a combination of new and archival optical and radio observations to attempt to better understand why some objects are detected as X-ray sources and others are not. We have also developed a morphological classification scheme for the optically identified SNRs and discussed the efficacy of this scheme as a predictor of X-ray detectability. Finally, we have compared the SNRs found in M33 to those that have been observed in the Galaxy and the Magellanic Clouds. Description: The strategy for the ChASeM33 survey has been described in detail by Plucinsky et al. (2008, Cat. J/ApJS/174/366). The survey comprises ACIS-I observations of seven overlapping fields which cover the inner region of M33 to a radius of about 18', or 4.3kpc. Data include not only those obtained by us as part of ChASeM33, between 2005 September and 2006 November, but also ACIS-I data from observations which are available from the Chandra archive (ObsIDs 1730 and 2023). Optical spectroscopy was used in support of the Chandra SNR analysis (see Note 6 of Table 3). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 94 137 M33 SNRs and SNR candidates - basic data table4.dat 51 131 M33 SNRs and SNR candidates - X-ray results
See also: J/ApJS/120/247 : Supernova remnants in M33 (Gordon+, 1999) J/A+A/426/11 : XMM-Newton survey of M33 (Pietsch+, 2004) J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006) J/ApJS/174/366 : Chandra ACIS survey of M33 (ChaSeM33) (Plucinsky+, 2008) http://www.lowell.edu/users/massey/lgsurvey : Online data from the LGGS Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 7 A7 --- Name Object name (<[LBW2010] NNN> in Simbad) 9- 15 A7 --- OName Other designation (G1) 17- 18 I2 h RAh Hour of right ascension (J2000) 20- 21 I2 min RAm Minute of right ascension (J2000) 23- 27 F5.2 s RAs Second of right ascension (J2000) 29 A1 --- DE- Declination sign (J2000) 30- 31 I2 deg DEd Degree of declination (J2000) 33- 34 I2 arcmin DEm Arcminute of declination (J2000) 36- 39 F4.1 arcsec DEs Arcsecond of declination (J2000) 41- 43 I3 pc Diam Diameter (1) 45- 46 A2 --- Mph [A"ABC ] Optical morphology (2) 48 I1 --- Env [1-3] Environment class (3) 50 A1 --- Rad [ync?] Radio source? (4) 52- 58 E7.2 mW/m2/arcsec2 SB Hα surface brightness (5) 60- 66 E7.2 10-7W LHa Hα luminosity (5) 68 A1 --- l_[NII] Limit flag on [NII] 69- 72 F4.2 --- [NII] ? [NII]/Hα flux ratio (6548,6583) 74- 77 F4.2 --- [SII] ? [SII]/Hα flux ratio (6717,6731) 79- 82 F4.2 --- [SII]r ? Line ratio of [SII]6717,6731 84- 90 A7 --- Ref Spectroscopic reference (6) 92- 94 A3 --- f_Ref [,a-c ] Flag on Ref (7)
Note (1): Objects have diameters ranging from 8 to 179pc; the median diameter is 44pc, corresponding to a middle-aged SNR. The SNR size was determined primarily from the LGGS (Local Group Galaxies Survey, carried out by Massey et al. (2006, Cat. J/AJ/131/2478, 2007, Cat. J/AJ/134/2474) using the 4m Mayall telescope and prime-focus Mosaic detector at KPNO) images, further informed by the X-ray data. We defined elliptical regions that best traced the optical shell, expanded slightly in a few cases to embrace X-ray emission that is apparently associated with the SNR (see Section 5.1). The "diameter" as defined and used in this paper is the geometric mean of the major and minor axes of this ellipse. All of the objects were clearly extended in the LGGS images. However, the error in measuring the diameter, which for a well-defined object is 0.5-1", clearly has a larger fractional effect on the small-diameter objects. For the poorly defined objects in morphology class C (Section 7.2), the size is highly uncertain. Note (2): Morphology classification as follows: A = well defined, nearly complete shells; A" = small (and typically bright) objects that may not show a shell structure but that are nevertheless clearly defined. B = partial shells, whose size can be estimated from the curvature of the visible portion of the shell; C = amorphous or poorly defined objects, sometimes a single filament. Note (3): Environment classification as follows: 1 = isolated from other nebulosity, 2 = within nebulosity, but easily separable from the potential contamination 3 = confused or difficult to isolate from the surrounding nebulosity. Note (4): Code as follows: y = reported by Gordon et al. (1999, Cat J/ApJS/120/247; <[GDK99] NNN> in Simbad) as a radio-detected SNR; c = detected by Gordon et al. and confirmed by our new radio observations; ? = claimed as a radio-detected SNR by Gordon et al. but seen in our higher-resolution data as radio emission arising from a nearby HII region or point source, not the SNR; n = not yet detected at radio wavelengths. As discussed in the text, because our radio observations were designed for studies of small-diameter SNRs, we did not expect to detect all of the SNRs detected by Gordon et al. (1999, Cat J/ApJS/120/247). Note (5): Both surface brightness and LHα include some contribution from [NII]6548,6583. Note (6): Optical spectroscopic references as follows: hecto = Multi-fiber system "Hectospec" used during several runs in autumn 2008 to observe over 130 ChASeM33 sources. MMT-BCS = In 2006 September and 2007 September, we used the long-slit CCD spectrograph known as the Blue Channel Spectrograph (BCS) to observe 14 SNR candidate using the MMT. G98 = Gordon et al., 1998ApJS..117...89G; <M33SNR NN> in Simbad. BK85 = Blair W.P. & Kirshner R.P. 1985ApJ...289..582B S93 = Smith et al., 1993ApJ...407..564S Note (7): Flags as follows: a = First spectroscopic confirmation that [SII]:Hα ratio supports a classification as an SNR. b = [SII]:Hα varies for two spectra of separate sections; average shown c = G98-83 has a low [SII]:Hα ratio for an SNR and this makes its identification as an SNR suspect.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 7 A7 --- Name Object name (<[LBW2010] NNN> in Simbad) 9- 15 A7 --- OName Other designation (G1) 17- 21 F5.1 ks Exp Exposure time 23- 25 F3.1 arcmin Ang Angle (1) 27- 32 F6.1 ct Cts Counts in the 0.35-2.0keV band 34- 37 F4.1 ct e_Cts Cts uncertainty 39 A1 --- l_Lx Limit flag on Lx (2) 40- 46 E7.2 --- Lx 0.35-2.0keV luminosity (2) 48- 51 F4.1 --- HR ? Hardness ratio (3)
Note (1): Characteristic off-axis angle at which this object was observed. Note (2): 2σ upper limits are shown for objects that were not detected. Note (3): Hardness ratio constructed from the ratio of (M-S)/Total counts, where S corresponds to 0.35-1.2keV counts, M to 1.2-2.6keV counts, and Total to 0.35-8keV counts.
Global notes: Note (G1): Other names or for new objects whether the object was initially suspected to be SNR based on optical or X-ray data. Names can be retrieved from the catalogs below: G98 = Gordon et al., 1998ApJS..117...89G; <M33SNR NN> in Simbad. All 98 objects plus three additional objects based on our assertion that G98-43, G98-57, and G98-97 are multiple SNRs. XMM = Pietsch et al., Cat. J/A+A/426/11; <[PMH2004] NNN> in Simbad. FL = Plucinsky et al., Cat. J/ApJS/174/366; <ChASeM33 NNN> in Simbad.
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 31-Jan-2011
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