The Origin of the Cosmic Gamma-Ray Background in the COMPTEL Energy Range

The spectrum of the cosmic gamma-ray background (CDG) has been measured in the energy range 0.8-30 MeV employing the Compton telescope COMPTEL on board the Compton Gamma Ray Observatory. The analysis is based on the identification of all major instrumental background lines as well as on a detailed study of the characteristics of the instantaneous instrumental continuum background. No evidence for an "MeV bump" could be found in the COMPTEL spectrum. Rather, the spectrum, well described by a power law, merges smoothly with spectra observed at higher and lower energies and is consistent with a transition from a softer to a harder component around a few MeV. The spectrum favours the superposed emission of unresolved point sources, such as AGN and supernovae, as the origin of the CDG over truly diffuse processes such as matter-antimatter annihilation.