Gamma-Ray Observations of Nucleosynthesis and Supernova Remnants

The CGRO sky survey identifies high-energy gamma-ray emission from the plane of the Galaxy as originating from cosmic-ray interactions with interstellar gas. Towards lower gamma-ray energy and the X-ray regime, specific sources become of increasing importance. The radioactivities of (26) Al and (44) Ti provide specific windows where nucleosynthesis sites can be isolated through gamma-ray surveys in the corresponding lines, thus focussing on one of the candidate source types. (26) Al sources most likely relate to massive stars, Wolf-Rayet winds and/or core-collapse supernovae appear responsible for the (26) Al in the interstellar medium. Other tracers of massive star locations in the Galaxy are employed to confirm (26) Al source types, comparing their spatial distribution to the 1.809 MeV emission. Observations in the (60) Fe lines, which would testify a dominating supernova origin, have not been feasible with sufficient sensitivity. In (44) Ti, the Cas A detection had confirmed the core-collapse origin of this isotope. A new and previously unknown supernova remnant appears in (44) Ti gamma -rays in the Vela region. Its overlap with a newly discovered X-ray supernova remnant poses interesting constraints.