Galactic gamma radiation : the contribution from discrete sources.

The contribution from discrete sources to the emission of galactic gamma rays is studied based on an analysis of the SAS II satellite data. The data are analyzed using cross-correlation techniques, and the results are interpreted using extensive Monte-Carlo simulations of the gamma-ray sky. These results are compared to earlier analyses based on the 2CG catalogue from satellite data. It is determined that most of the 2CG sources are visible as flux-excesses with good agreement between the fluxes measured for the common sources. It is found that most of the observed emission is due to diffuse structures of interstellar atomic and molecular hydrogen with a small contribution from genuine discrete sources. The data indicate that a source contribution to the galactic plane flux of the order of 10 percent, and up to 70 percent of the 2CG sources could be due to cosmic ray irradiation processes or statistical fluctuations.