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M31CXOXRAY - M31 Central Region Chandra X-Ray Point Source Catalog

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Overview

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 ~2x10^35 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^-4 ct/s, which is equivalent to an X-ray luminosity of about 2 x 10^35 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 ftp://cdsarc.u-strasbg.fr/pub/cats/J/ApJ/577/738/ (table4.dat & table5.dat).


Catalog Bibcode

2002ApJ...577..738K

References

X-ray point sources in the central region of M31 as seen by Chandra.
    Kong A.K.H., Garcia M.R., Primini F.A., Murray S.S., di Stefano R.,
    McClintock J.E.
   <Astrophys. J. 577, 738 (2002)>
   =2002ApJ...577..738K

Provenance

This table was created by the HEASARC in October 2004 based on CDS Catalog J/ApJ/577/738/table2.dat.

Parameters

Source_Number
The catalog source number, using a nomenclature scheme based on optical studies (Morton et al. 1977, ApJ, 212, 13: a similar classification was also used by Trinchieri and Fabbiano 1991, ApJ, 382, 82). The source numbers have a prefix of either 'r1', 'r2', or 'r3'. The 'r1' sources are located in the central 2'x2' or `inner bulge' region. The 'r2' sources are located in the central 8'x8' region, excluding the inner bulge region; the authors refer to this annular region as the `outer bulge'. The 'r3' sources are located outside the central 8'x8' region in the `disk' region.

Name
The IAU-approved name for a Chandra X-ray source in M 31, of the form CXOM31 JHHMMSS.s+DDMMSS.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 coordinates and to a precision of 0.001 seconds of time in the original form of the catalog.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 coordinates and to a precision of 0.01 arcseconds in the original form of the catalog.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The positional error, in arcseconds.

Counts
The net counts in the X-ray source.

Count_Rate
The count rate of the X-ray source, in ct/s, corrected for exposure, background variation and instrumental point spread function. Source count rates were determined via aperture photometry. The radius of the aperture was varied with average off-axis angle in order to match the 90% encircled energy function. The average off-axis angle was computed for each source based on the off-axis angles of the 8 observations weighted by their exposure times. The extraction radius varied from ~1" near the aimpoint to ~17" for the sources with the largest off-axis angles. Background was extracted from an annulus centered on each source. In some cases, for example in the nuclear region, the extraction region was modified to avoid nearby sources. It was also necessary to modify the extraction radius for some faint sources that were close to more liminous sources.

Count_Rate_Error
The one-sigma error in the count rate, in ct/s.

Hardness_Ratio_1
The medium-soft hardness ratio HR1 = (M-S)/(M+S) of the X-ray source, where S is the counts in the 0.3-1.0 keV energy band and M is the counts in the 1-2 keV energy band.

Hardness_Ratio_1_Error
The error in the hardness ratio HR1.

Hardness_Ratio_2
The hard-soft hardness ratio HR2 = (H-S)/(H+S) of the X-ray source, where S is the counts in the 0.3-1.0 keV energy band and H is the counts in the 2-7 keV energy band.

Hardness_Ratio_2_Error
The error in the hardness ratio HR2.

Xray_Luminosity
The 0.3-7 keV luminosity of the X-ray source, in erg/s. The conversion into X-ray luminosity assumed an absorbed power-law spectrum with a photon index of 1.7 and a hydrogen column density of 10^21 atoms/cm^2, which is the typical spectrum of a point source in M 31 according to Shirey et al. (2001, A&A, 365, L195).

Note_Codes
A parameter containing notes codes as follows:

  Value   Meaning

      e = Extragalactic object
      f = Foreground star
      g = Globular Cluster
      p = Planetary nebula
      r = ROSAT HRI source
      s = Supernova remnant
      v = Variable
     sv = Spectral variable
      t = Transient
  

Contact Person

Questions regarding the M31CXOXRAY database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 8-Nov-2004