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Description
One hundred fifty-five (the abstract in the paper erroneously states the number to be 154) discrete, non-nuclear, ultraluminous X-ray (ULX) sources, with spectroscopically determined intrinsic X-ray luminosities greater than 10<sup>39</sup> erg/s, have been identified in 82 galaxies that were observed with Chandra's Advanced CCD Imaging Spectrometer (ACIS). Positions, X-ray luminosities, and spectral and timing characteristics of these ULXs are contained in this table. Eighty-three percent of ULX candidates have spectra that can be described as absorbed power laws with mean index Gamma = 1.74 and column density N<sub>H</sub> = 2.24 x 10<sup>21</sup> atoms cm<sup>-2</sup>, or ~5 times the average Galactic column. About 20% of the ULXs have much steeper indices indicative of a soft, and likely thermal, spectrum. The locations of ULXs in their host galaxies are strongly peaked toward their galaxy centers. The deprojected radial distribution of the ULX candidates is somewhat steeper than an exponential disk, indistinguishable from that of the weaker sources. About 5%-15% of ULX candidates are variable during the Chandra observations (which average 39.5 ks). Comparison of the cumulative X-ray luminosity functions of the ULXs to Chandra Deep Field results suggests ~25% of the sources may be background objects, including 14% of the ULX candidates in the sample of spiral galaxies and 44% of those in elliptical galaxies, implying the elliptical galaxy ULX population is severely compromised by background active galactic nuclei. Correlations with host galaxy properties confirm the number and total X-ray luminosity of the ULXs are associated with recent star formation and with galaxy merging and interactions. The preponderance of ULXs in star-forming galaxies as well as their similarities to less-luminous sources suggest they originate in a young but short-lived population such as the high-mass X-ray binaries, with a smaller contribution (based on spectral slope) from recent supernovae. The number of ULXs in elliptical galaxies scales with host galaxy mass and can be explained most simply as the high-luminosity end of the low-mass X-ray binary population. This table was created by the HEASARC in March 2007 based on CDS catalog J/ApJS/154/519 file table2.dat. This is a service provided by NASA HEASARC .
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