Hard X-ray and gamma-rays from supernovae

The hard electromagnetic radiation produced by and accompanying the explosion of supernovae is discussed. This radiation may have three origins: (i) the eruption of the shock wave from the surface of the star; (ii) radioactive decay of unstable isotopes produced during the explosion; and (iii) gamma-rays produced by neutrino annihilation following accretion-induced collapse. Though the latter has been proposed as a mechanism for making cosmological gamma-ray bursts, it is shown that this is unlikely.