Nuclear and gamma-ray production by supernova ejecta

The fastest components of supernova ejecta can have have particle energies above the thresholds for γ-ray production and for nuclear spallation. Thus we expect the fast ejecta to create a γ-ray echo of the explosion as they traverse the circumstellar and interstellar medium. Further, as the fastest particles come from the outermost layers of the supernova progenitor, they may provide a signature of their composition. It is proposed that the very unusual COMPTEL observations in Orion could arise from a supernova with an unusual outer composition: namely, a CO core explosion occurring in the dense Orion cloud. Fast particle spectra are computed from both analytical and numerical supernova models, and are found to have features that are quite universal. The observational and nucleosynthetic implications of this mechanism are discussed, both for Orion, and for supernovae generally.