Chan/M31 ivo://nasa.heasarc/m31cxoxray NASA/GSFC HEASARC Kong et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source This table countains the M 31 Central Region Catalog of Chandra X-Ray Point Sources. It is based on Chandra observations of the central region of M 31. By combining eight Chandra ACIS-I observations which were taken between 1999 and 2001, the authors have identified 204 X-ray sources within the central ~17'x17' region of M 31, with a detection limit of ~2x10<sup>35</sup> erg/s. Of these 204 X-ray sources, 22 are identified with globular clusters, two with supernova remnants, nine with planetary nebulae, and nine with supersoft sources. By comparing individual images, about 50% of the sources were found to be variable on timescales of months. The authors also found 13 transients, with light curves showing a variety of shapes. They also extracted the energy spectra of the 20 brightest sources; they can be well fitted by a single power law with a mean photon index of 1.8. The spectral shapes of 12 sources were variable, suggesting that they went through state changes. All sources in the catalog have S/N > 2.5 and only five have S/N < 3.0. The detection limit for the sources varies across the image due to the variation of exposure time, background, and instrumental PSF, and is highest near the edges, where the PSF broadens rapidly and the exposure time is lowest. Over the inner 4' of the field, the detection limit is 2.1 x 10<sup>-4</sup> ct/s, which is equivalent to an X-ray luminosity of about 2 x 10<sup>35</sup> erg/s. Additional information about optical identifications and cross-correlated ROSAT X-ray sources not provided in this HEASARC table is available in the published paper (Tables 4 and 5) and/or the CDS at <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/577/738/">https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/577/738/</a> (table4.dat & table5.dat). This table was created by the HEASARC in October 2004 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/577/738/table2.dat">CDS Catalog J/ApJ/577/738/table2.dat</a>. This is a service provided by NASA HEASARC . 2002ApJ...577..738K https://heasarc.gsfc.nasa.gov/W3Browse/all/m31cxoxray.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=m31cxoxray& GET text/xml 180 99999 true 10.62027917 41.07638333 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=m31cxoxray GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_m31cxoxray&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public m31cxoxray M 31 Central Region Chandra X-Ray Point Source Catalog name Chandra Source Designation (CXOM31 JHHMMSS.s+DDMMSS) meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable error_radius Positional Error (arcsec) arcsec stat.error;pos float nullable count_rate Count Rate (ct/s) ct/s phot.count;em.X-ray double nullable count_rate_error Error in Count Rate (ct/s) ct/s stat.error;phot.count;em.X-ray double nullable counts Net Counts ct short nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable source_number Catalog Entry Identifier meta.id char nullable hardness_ratio_1_error Error in First Hardness Ratio stat.error;phot.count;arith.ratio float nullable hardness_ratio_2 Second Hardness Ratio phot.count;arith.ratio float nullable hardness_ratio_1 First Hardness Ratio phot.count;arith.ratio float nullable note_codes Additional Notes meta.note char nullable xray_luminosity The 0.3-7keV Luminosity (erg/s) erg/s phys.luminosity;em.X-ray.medium double nullable lii Galactic Longitude degree pos.galactic.lon double nullable hardness_ratio_2_error Error in Second Hardness Ratio stat.error;phot.count;arith.ratio float nullable bii Galactic Latitude degree pos.galactic.lat double nullable