Contribution of Unresolved Point Sources to the Diffuse X-ray Background below 1 keV

TL;DR

This study analyzes X-ray point sources below 1 keV using XMM-Newton data, revealing their contribution to the diffuse X-ray background and identifying an excess flux at 0.5 keV suggesting additional weak sources.

Contribution

It provides new insights into the contribution of unresolved point sources to the diffuse X-ray background below 1 keV, including the detection of an excess flux at 0.5 keV.

Findings

Detected an excess flux at 0.5 keV in faint sources

Quantified the contribution of point sources to the 3/4 keV background

Found a general property of excess flux across multiple fields

Abstract

We present here the analysis of X-rays 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. The average field of all the exposures is 0.09 deg^-2. We reached an average flux sensitivity of 5.8x10^-16 erg s^-1 cm^-2 in the soft band (0.5-2.0 keV) and 2.5x10^-16 erg s^-1 cm^-2 in the very soft band (0.4-0.6 keV). In this paper we discuss the logN-logS 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 diffuse X-ray Background in the 3/4 keV band.