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[5.14] A Comparison Between Spectral Properties of ULXs and Luminous X-ray Binaries

C. T. Berghea, E. J. M. Colbert (CUA), T. P. Roberts (Leicester)

What is special about the 10³⁹ erg~s^-1 limit that is used to define the ULX class? We investigate this question by analyzing Chandra X-ray spectra of 71 X-ray bright point sources from nearby galaxies. Fifty-one of these sources are ULXs (L_X(0.3-8.0~keV) \ge 10³⁹ erg~s^-1), and 20 sources (our comparison sample) are less-luminous X-ray binaries with L_X(0.3-8.0~keV)~= 10^38-39 erg~s^-1. Our sample objects were selected from the Chandra archive to have \ge1000 counts and thus represent the highest quality spectra in the Chandra archives for extragalactic X-ray binaries and ULXs. We fit the spectra with one-component models (e.g., cold absorption with power-law, or cold absorption with multi-colored disk blackbody) and two-component models (e.g. absorption with both a power-law and a multi colored disk blackbody). A crude measure of the spectral states of the sources are determined observationally by calibrating the strength of the disk (blackbody) and coronal (power-law) components. These results are then use to determine if spectral properties of the ULXs are statistically distinct from those of the comparison objects, which are assumed to be ``normal'' black-hole X-ray binaries.

The author(s) of this abstract have provided an email address for comments about the abstract: 79berghea@cua.edu

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Bulletin of the American Astronomical Society, 36 #2
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