A Chandra High Resolution Camera Observation of X-Ray Point Sources in M31

We present results from a 47 ks observation of the Andromeda galaxy, M31, using the High Resolution Camera of the Chandra X-Ray Observatory. We detect 142 point sources spanning 3 orders of magnitude in luminosity, from L_X=2×10³⁵ to 2×10³⁸ ergs s^-1 in the 0.1-10 keV band. The X-ray source location accuracy is better than 1" in the central regions of the galaxy. One source lies within 1.3" of SN 1885 but does not coincide with the UV absorption feature identified as the supernova remnant. However, there is an optical transient, which is likely an optical nova, at the location of the X-ray source. There is a weak source, L_X~4×10³⁶ ergs cm² s^-1, coincident with the nucleus of M31 and 14 sources coincident with globular clusters. Our observation has very high efficiency down to luminosities of 1.5×10³⁶ ergs s^-1 for sources within 5' of the nucleus. Comparing with a ROSAT observation made 11 yr earlier, we find that 0.46+/-0.26 of the sources with L_X>5×10³⁶ ergs s^-1 are variable. We find no evidence for X-ray pulsars in this region, indicating that the population is likely dominated by low-mass X-ray binaries. The source density radial profile follows a power-law distribution with an exponent of 1.25+/-0.10 and is inconsistent with the optical surface brightness profile. The X-ray point-source luminosity function is well fitted by a differential broken power law with a break at a luminosity of (4.5^+1.1_-2.2)×10³⁷ ergs s^-1. The luminosity function is consistent with a model of an aging population of X-ray binaries.