Cosmic gamma rays.

Evidence on high-energy galactic cosmic gamma-radiation, correlated with nonthermal radiation at the RF end of the spectrum, is examined for information on the origin of cosmic rays, on the large-scale structure of the galaxy and on the existence of a galactic halo (obscured by optically opaque dust clouds), on pulsar behavior, and on the early universe. Some correlation of gamma-radiation with dense gas clouds and frequency of supernova explosions, and specifically the Crab and Vela remnants, is noted. Spark-chamber data from the SAS-2 and COS-B satellites and experimental techniques to resolve uncertainties in observations of cosmic gamma-radiation are discussed. Isotropic low-energy gamma-radiation, possibly of extragalactic origin, is examined as a test of theories on evolution of the universe.