Contribution of unresolved point sources to the diffuse x-ray background below 1 keV

Abstract

We present here the analysis of X-ray point sources detected in several observations available in the XMM-Newton public archive. We focused, in particular, on energies below 1 keV, which are of particular relevance to the understanding of the diffuse X-ray background (DXB). The average field of all the exposures is 0.09deg-2. We reached an average flux sensitivity of 5.8 × 10-16ergs-1cm-2 in the soft band (0.5-2.0 keV) and 2.5 × 10-16ergs-1cm-2 in the very soft band (0.4-0.6 keV). In this paper, we discuss the log N-log S results, the contribution to the integrated X-ray sky flux, and the properties of the cumulative spectrum from all sources. In particular, we found an excess flux at around 0.5 keV in the composite spectrum of faint sources. The excess seems to be a general property of all the fields observed suggesting an additional class of weak sources is contributing to the X-ray emission at these energies. Combining our results with previous investigations, we have also quantified the contribution of the individual components of the DXB in the 3/4 keV band. © 2009. The American Astronomical Society. All rights reserved.