Diffuse galactic annihilation radiation and the present rate of galactic nucleosynthesis

Abstract

Observations of positron annihilation radiation from the inner region of the Galaxy show that there are two components of the radiation: a steady, diffuse galactic disk component and a variable component from discrete, presumably compact sources. Here we focus on the observations of the diffuse galactic emission and their implications for the present galactic rate of iron nucleosynthesis. We discuss recent calculations of the nucleosynthetic yield and the survival of positrons in supernova ejecta, expected from current supernova models. These calculations show that positrons from the β + decay of nucleosynthetic 56Co→ 56Fe→, 44Sc→ 44→ 44 Ca, and 26Al → 26Mg, can easily account for the observed galactic annihilation radiation, and they suggest a present galactic rate of 56Fe nucleosynthesis of ≈(0.8 ± 0.5) M ⊙ per 100 yr.