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M87CXO - M 87 Chandra X-Ray Point Source Catalog


The ACIS instrument on board the Chandra X-Ray Observatory has been used to carry out the first systematic study of low-mass X-ray binaries (LMXBs) in M 87 (NGC 4486), the giant elliptical galaxy near the dynamical center of the Virgo Cluster. These images - with a total exposure time of 154 ks - are the deepest X-ray observations obtained as of 2004 of M 87. The authors identified 174 X-ray point sources, (contained in this Browse table) of which ~ 150 are likely LMXBs. This LMXB catalog was combined with deep F475W and F850LP images taken with ACS on the Hubble Space Telescope (HST) (as part of the ACS Virgo Cluster Survey) to examine the connection between LMXBs and globular clusters in M87. Of the 1688 globular clusters in the authors' catalog, a fraction f_X = 3.6% 0.5% contain an LMXB.

M 87 (NGC 4486) was observed with the Chandra Advanced CCD Imaging Spectrometer (ACIS) for 121 ks on 2002 July 5-6. In this table, only the S3 chip data are used. The data were processed following the CIAO data reduction threads, including a correction for charge transfer inefficiency (CTI). In addition, the authors used 38 ks of archival ACIS observations of M 87 taken on 2000 July 29. These data were processed in a fashion similar to the 2002 July data, except that no CTI correction was possible because the data were telemetered in graded mode. All reductions were carried out with CIAO, version 2.3, coupled with CALDB, version 2.21. In order to combine the event files into a single image for point-source detection, the authors obtained relative offsets by matching the celestial coordinates of two X-ray point sources. The relative offset was ~ 0.5". The total exposure time of the co-added image, excluding four background flares totaling ~ 2.5 ks, was 154 ks.

Catalog Bibcode



The ACS Virgo Cluster Survey. III. Chandra and Hubble space telescope
observations of low-mass X-ray binaries and globular clusters in M87.
    Jordan A., Cote P., Ferrarese L., Blakeslee J.P., Mei S., Merritt D.,
    Milosavljevic M., Peng E.W., Tonry J.L., West M.J.
   <Astrophys. J., 613, 279-301 (2004)>


This table was created by the HEASARC in March 2007 based on the CDS table J/ApJ/613/279, file table1.dat.


A running number for the X-ray source in order of increasing J2000.0 Right Ascension within the field.

The name of the Chandra X-ray source using the standard 'CXOU' prefix and the J2000.0 position (JHHMMSS.s+DDMMSS).

The alternative name of the X-ray source using the '[JCF2004]' prefix followed by the X-ray source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 seconds of time in the original table.

The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 1 arcsecond in the original table.

The Galactic Longitude of the X-ray source.

The Galactic Latitude of the X-ray source.

The background-corrected count rate in the 0.3 to 10 keV energy range of the X-ray source, in ct/s.

The X-ray luminosity of the source in the 0.3 - 10 keV energy band, in erg/s. The composite, background-subtracted source spectra for the 2000 and 2002 data sets were fitted simultaneously with XSPEC, version 11.2.0. The spectral energy distribution was assumed to have a single photon power-law behavior ~ E^-kappa. The Galactic hydrogen column density was held fixed at N_H = 2.5 x 10^20 cm^-2 in the fit; channels with energy less then 0.7 keV and greater than 4 keV were excluded from the fit. The best-fit power-law exponent was kappa = 1.64 (90% confidence uncertainties), with a reduced chi-squared of 1.032 with 218 degrees of freedom, typical of the values found for point sources in other nearby galaxies. This best-fit model was used to convert the observed counts to unabsorbed luminosities L_x over the range 0.3 - 10 keV, assuming that all the sources were at the 16 Mpc distance of M87. The resulting conversion factor was 1.4 x 10^41 ergs ct^-1.

The 2-1 hardness ratio H_21=(M-S)/(M+S), where S and M are the counts in the soft (0.3 - 1 keV) and medium (1 - 2 keV) energy bands, respectively.

The 3-1 hardness ratio H_31=(H-S)/(H+S), where H and S are the counts in the soft (0.3 - 1 keV) and hard (1 - 10 keV) energy bands, respectively.

This parameter is a flag which indicates whether or not the position of the X-ray source fell within the field of view of the ACS observations

This field contains comments on the classification of the various optical sources.

Contact Person

Questions regarding the M87CXO database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk