Journal
ASTROPHYSICAL JOURNAL
Volume 588, Issue 2, Pages 696-703Publisher
IOP PUBLISHING LTD
DOI: 10.1086/374335
Keywords
cosmology : observations; diffuse radiation; surveys; X-rays : diffuse background; X-rays : general
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We present the X-ray source number counts in two energy bands (0.5-2 and 2-10 keV) from a very large source sample: we combine data of six different surveys, both shallow wide-field and deep pencil-beam, performed with three different satellites (ROSAT, Chandra, and XMM-Newton). The sample covers with good statistics the largest possible flux range so far: 2.4x10(-17) to 10(-11) ergs s(-1) cm(-2) in the soft band and 2.1x10(-16) to 8x10(-12) ergs s(-1) cm(-2) in the hard band. Integrating the flux distributions over this range and taking into account the (small) contribution of the brightest sources, we derive the flux density generated by discrete sources in both bands. After a critical review of the literature values of the total cosmic X-ray background (CXB) we conclude that, with the present data, 94.3(-6.7)(+7.0%) and 88.8(-6.6)(+7.8%) of the soft and hard CXB can be ascribed to discrete source emission. If we extrapolate the analytical form of the log N-log S distribution beyond the flux limit of our catalog in the soft band we find that the flux from discrete sources at similar to3x10(-18) ergs s(-1) cm(-2) is consistent with the entire CXB, whereas in the hard band it accounts for only 93% of the total CXB at most, hinting at a faint and obscured population to arise at even fainter fluxes.
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