On the X-Ray Source Luminosity Distributions in the Bulge and Disk of M31: First Results from the XMM-Newton Survey

Abstract

We present luminosity distributions for the X-ray sources detected with XMM-Newton in the bulge and disk of the Andromeda galaxy (M31). The disk is clearly lacking the bright sources that dominate X-ray emission from the bulge. This is the first convincing evidence of a difference between bulge and disk X-ray populations in M31. Our results are in good qualitative agreement with the luminosity distributions for low- and high-mass X-ray binaries recently obtained by Grimm, Gilfanov, & Sunyaev for our Galaxy. The data presented here confirm that X-ray population of the disk of M31 is dominated by faint high-mass X-ray binary sources, while the bulge is populated with bright low-mass X-ray binaries.