Galactic X-ray source populations

Abstract

The landscape of Galactic X-ray sources made of accreting binaries, isolated objects and active stellar coronae has been significantly modified by the advent of the Chandra, XMM-Newton and INTEGRAL satellites. New types of relatively low X-ray luminosity X-ray binaries have been unveiled in the Galactic disc, while deep observations of the central regions have revealed large numbers of X-ray binaries of so far poorly constrained nature. Because of the high spatial resolution needed and faint X-ray luminosities generally emitted, studying the dependency of the X-ray source composition with parent stellar population, Galactic disc, bulge, nuclear bulge, etc., is only practicable in our Galaxy. The evolutionary links between low L_X X-ray binaries and classical X-ray luminous accreting systems are still open in many cases. In addition, the important question of the nature of the compact sources contributing to the Galactic ridge hard X-ray emission remains unresolved. We review the most important results gathered by XMM-Newton over the last years in this domain and show how future observations could be instrumental in addressing several of these issues.