M31 Chandra X-ray point sources

By combining eight Chandra ACIS-I observations taken between 1999 and 2001, we have identified 204 X-ray sources within the central ~17'x17' region of M31, with a detection limit of ~2x10^35^erg/s. Of these 204 sources, 22 are identified with globular clusters, two with supernova remnants, nine with planetary nebulae, and nine with supersoft sources.

By comparing individual images, about 50% of the sources are variable on timescales of months. We also found 13 transients, with light curves showing a variety of shapes. We also extracted the energy spectra of the 20 brightest sources; they can be well fitted by a single power law with a mean photon index of 1.8.