Gamma-Ray Lines and High-Energy Sources

Gamma-ray lines may provide diagnostic information on cosmic high energy sources: They originate from the decay of radioactive nucleosynthesis products, from positron annihilations, and from atomic nuclei which have been excited by energetic collisions. Shortlived isotopes such as 56Ni and 44Ti are produced in supernovae, their gamma-ray line intensities and line profiles reflect kinematics and morphology of the exploding star. Long-lived isotopes such as 26Al, and also the positron annihilation gamma-rays, can be used to study propagation processes in the interstellar medium near high-energy sources, complementing observational time scales at the long end of the range of interest. Such annihilation emission and also lines from excited nuclei near accreting compact stars should reflect energetic conditions at environments which are believed to inject suprathermal particles into relativistic accelerators to produce cosmic rays. New INTEGRAL measurements on these frontiers are discussed in this paper