The Next Nearest Black Holes: Chandra and HST Observations of X-ray sources in M31

Abstract

From October 1999 to the present Chandra has taken nearly monthly snap-shot observations of M31. The first 3 years of this dataset in combination with deeper but less frequent XMM observations has allowed the detection of 45 X-ray transients within M31. By analogy to our Galaxy, many of these transients are likely black hole candidates. We have indentified a few optical counterparts of these possible black holes via simultaneous HST imaging. The census allows a study of the endpoints of stellar evolution in our nearest neighbor galaxy. When stacked, the observations also allow a deep study of the M31 X-ray source population, which turns up a few surprises. The supermassive black hole in the center of M31 is the next nearest one after Sgr A*. Chandra and HST observations allow the detection of a weak X-ray source at the position of this SMBH. These observations provide some of the most secure and severe limitations on accretion in SMBH.