Gamma-Ray Observations and the Large-Scale Structure of the Galaxy

Gamma ray astronomical explorations by the SAS-2 and COS-B satellites are discussed, and the latitude distribution of gamma radiation using COS-B data is presented. The strongest feature of the gamma ray sky is the overwhelming emission of the galactic disc. The gamma ray disc seems as thin as the gaseous, though it may not extend well beyond the solar circle; structural features are clearly apparent. Spectral characteristics of the galactic gamma radiation reveal that in the local interstellar medium the main emission mechanisms involve high energy nucleons and electrons (bremsstrahlung), while an analysis of the large scale structure of the gamma ray disc (Caraveo and Paul, 1978) leads to distinct radial distributions of the gamma ray emissivity for both 'positive' (broad peak at 5-6 kpc from the galactic center) and 'negative' longitudes (two peaks, at 4-5 kpc and at 7-8 kpc)