Study of High Luminosity X-Ray Sources in External Galaxies (M-31)

Einstein Observatory observations of high-luminosity X-ray sources in M 31 are discussed. Images obtained from the Einstein IPC and HRI detectors reveal up to 45 individual X-ray sources in the galaxy, of total luminosity 2.3 x 10 to the 39th erg/sec. Identifications have been made of source positions with those of supernova remnants, globular clusters, and possibly the galactic nucleus. The X-ray source population can also be divided into three groups: globular clusters, inner bulge sources and population I objects, which are observed to be correlated with H I features in spiral arms. The bulge sources, which occur in the central 2 arcmin of the nucleus and account for about 1/3 of M 31 X-ray emission, are much more numerous in M 31 than in the Galaxy, and can not be accounted for by evolutionary models of Galactic bulge sources.