Interstellar Gamma Ray Lines from Low Energy Cosmic Ray Interactions

Evidence for the existence of low energy cosmic rays in the Galaxy comes from the COMPTEL observations of gamma ray line emission from Orion, and also from light element abundance data which seem to suggest a low energy rather than a relativistic Galactic cosmic ray origin for most of the light elements. The Orion and light isotope data are more consistent with a composition that is depleted in protons and $\alpha$ particles than with one which is similar to that of the Galactic cosmic rays. This low energy cosmic ray phenomenon appears to be highly localized in space and time in the Galaxy, and is probably associated with star formation regions similar to Orion.