Ultraluminous X-ray Sources in Andromeda Galaxy: Two Recent Discoveries and their Implications

Ultraluminous X-ray sources are believed to be associated with X-ray binaries, in which an accreting black hole generates X-ray luminosities in excess of 10 erg/s. The nature of the companion star and the underlying physics of the accretion process is not yet established with certainty. In particular, whether or not the accretion is super/sub Eddington is an open question, as is the mass of the companion star. We discuss the first two ULXs recently discovered in M31 and investigate the nature of their underlying sources. We present the X-ray observations for ULX-1 in detail and discuss its implications for its accretor. We also considered the positions of both ULX sources in the context of their hypothetical association with either High Mass X-ray Binaries and Low Mass X-ray Binaries. We construct a simple disk plus bulge model to test their association with starlight and use IR images from Spitzer to investigate their possible link to star formation. We find that the position of these two sources more strongly supports scenarios in which the companion is a high mass star. Using the data obtained with XMM-Newton, Swift and Chandra, we infer that the underlying source for ULX-1 is a 13 M black hole under the assumption that it is non-spinning. The combined study of X-ray properties and the spatial distribution presented in this thesis argue in favor of stellar mass black holes accreting at near Eddington rates from high mass companions.