Contribution of supernova gamma-rays to the gamma-ray background emission

Diffuse gamma -ray background emission has been observed by a number of sat ellites and balloons. The spectrum spreads over a wide range of photon ener gies, and the emission is almost isotropic. Although the origin of diffuse gamma -ray background emission is still unclear, some candidates are sugges ted, such as Seyfert galaxies, blazars, and type-la supernovae. The type-la supernovae synthesize a large amount of Ni-56, which emit gamma -ray photo ns while decaying into Co-56 and then to Fe-56, and thus emit strong gamma -rays of energy around I MeV. We estimate the intensity of the diffuse gamm a -ray background emission from supernovae, and compare the result with the recent observation of COMPTEL. The resultant spectrum is too small to expl ain the observation, because it is only 10% of the observed flux, implying contributions from other sources.