Bright X-Ray Sources in M31 Globular Clusters

R. DiStefano, (CfA) A.K.H. Kong , (CfA), M. R. Garcia , (CfA), P. Barmby (CfA), J. Greiner (AIP, Potsdam), S.S. Murray , F.A. Primini (CfA)

[Contributed talk, 15min.]


We have conducted Chandra observations of $\sim 900$ square arcmin ($\sim 46$ kpc2) of M31, and find that the most luminous X-ray sources in most of our fields are in globular clusters (GCs). Of the 30 GC X-ray sources in our fields, 17 are newly discovered. Approximately 1/3 of all the sources have $L_x([0.5-7]\, keV) > 10^{37}$ ergs s-1; approximately 1/10 of all the sources have $L_x([0.5-7]\, keV)$ close to or above 1038 ergs s-1. The most luminous source, in the globular cluster Bo 375, is consistently observed to have Lx greater than $2\times 10^{38}$ergs s-1. In this talk we:

(1) describe the data,

(2) consider models that might apply to the highly luminous GC sources in M31: are the sources composites? are they accreting black holes? is the radiation beamed?

(3) explore the reasons why GCs in M31 house a population of X-ray sources that outshine those of our own Galaxy.

Our results on M31 GCs have implications that will help us to better model the processes that produce X-ray binaries in the GCs of our own and other galaxies. They suggest clues to the relationships between a galaxy's characteristics and history and the X-ray binary population of its GCs. In this sense, M31's GCs provide a bridge between the Milky Way's GC system and the GC systems of other galaxies.



Himel Ghosh