Cosmic diffuse gamma-rays at medium energies

Abstract

Cosmic diffuse gamma-ray fluxes have been measured in six energy intervals from 2 to 25 MeV with a balloon-borne gamma-ray telescope. It is found that the observed fluxes are compatible with an energy distribution of 0.0265 times E to the -2.08 (photon/sq cm-s-sr-MeV) at lower energies and steepen at higher energies to meet a power law of 0.017 (E/MeV) to the -2.4. No deviation of the gamma-ray flux from isotropy is observed for five different times during the balloon flight for 10-deg intervals up to 50 deg from the zenith and at celestial coordinates varying from latitude -27 deg, longitude 102 deg to latitude 56 deg, longitude 195 deg, excluding the region in the galactic-anticenter direction. Upper limits to fluxes of 3-25-MeV gamma rays are deduced for a number of possible galactic and extragalactic sources.