ABSTRACT

Thanks to their angular resolution and collecting area, Chandra and XMM/Newton have made it possible to study the x-ray source population of M31 at a level of detail previously impossible outside the Milky Way and Magellanic Clouds. The objective of this study is an unbiased view of the source population in a galaxy that is in many ways the twin of our own, without the distance confusion and interstellar absorption that plague Galactic observations. The XMM survey has so far detected 450 sources down to 10^35 ergs s-1. The luminosity distribution shows a clear difference between the bulge and the disk, and evidence for a roll-over at high luminosities that has been ascribed to the shorter life of high-luminosity sources. 34 sources have been detected in globular clusters; 7 of these are brighter than the brightest globular cluster x-ray source in our own galaxy. Although numerous transient and variable sources have been detected, only two periodic objects have been found so far. The correlation of the x-ray population with star-forming regions and individual optical counterparts is just beginning.