ROSAT OBSERVATIONS OF THE LUMINOUS X-RAY SOURCES IN M51

Our an analysis of a 24 ks ROSAT Position Sensitive Proportional Count er image of the interacting galaxies NGC 5194 (M51) and NGC 5195 shows that X-ray emission is distributed across the whole of NGC 5194. In a ddition to the diffuse emission and a bright nuclear region, eight ind ividual sources were detected with 0.2-2.2 keV luminosities from 5 to 29 x 10(38) ergs s(-1), more than 10 times higher than typical bright Galactic X-ray sources. The energy distribution of the luminous source s can be characterized by bremsstrahlung spectra with temperatures aro und 1 keV and low-energy absorption exceeding that expected from our G alaxy. Two sources lie in an inner spiral arm, while five lie along th e outer edges of the outer spiral arms. Four sources (R1, R2, R4, and R6) lie in or near regions of recent star formation as indicated by H II regions or CO emission from molecular clouds. However, for three of the X-ray sources which fall on the outer edge of the spiral arms (R3 , R7, and R8), there is little or no associated CO or H alpha emission . We discuss the origin of the luminous X-ray sources as possibly aris ing from either massive black holes in binary star systems, supernova remnants, or hot gas associated with star-forming regions.