Celestial diffuse gamma-ray emission observed by SAS-2 and its interpretation

Abstract

A clearly established diffuse celestial gamma-ray component was seen by SAS-2 above 35 MeV, after examining several regions of the sky at different latitudes, including the north celestial pole. For energies above 100 MeV the gamma ray results are consistent with an equation of the form I(b)=C1+C2/sin b with the second term being dominant, suggesting that the radiation above 100 MeV comes largely from the local regions of the galactic disk. Between 35 and 100 MeV, a similar equation is also a reasonable representation of the data, but here the two terms are comparable, with the first, or isotropic term, actually being the larger one. In addition to indicating that the diffuse radiation is partially galactic, these results imply a steepness for the energy spectrum of the diffuse isotropic component which places significant constraints on possible theoretical models of this radiation.