Gamma-Ray Observations of Starburst Galaxies

The supernova rate in starburst galaxies has been estimated to be on the order of ten to twenty times the supernova rate in our Galaxy. If the dominant acceleration sites of cosmic rays are supernova remnants then the cosmic ray density in starburst galaxies should also be proportionally higher. This implies that the diffuse gamma-ray emission from starburst galaxies can be used to directly estimate the cosmic ray density in these objects. Data from EGRET gamma-ray observations of the nearby starburst galaxies M82 and NGC 253 for CGRO cycles 1 through 5 (1991 April through 1996 October) has been analyzed using point-source likelihood techniques. The results of this analysis will be presented.