Science and Detection Prospects of Line Emission in the MeV Regime

Carolyn Kierans

NASA GSFC

Gamma-ray line emissions provide unique signatures of stellar and explosive nucleosynthesis and the propagation of low-energy cosmic rays in our Galaxy. The signature of positron annihilation at 511 keV was the first gamma-ray line to be detected as originating outside of our solar system. After 50 years of observations, the Galactic sources of positrons are still unconfirmed and the origin of this line remains one of the pioneering topics in gamma-ray astronomy. Nuclear emission lines from isotopes created in massive stars and their supernovae, such as Fe-60, Al-26 and Ti-44, allow for fingerprint-like probes into stellar structure and evolution, a tool which has yet to be fully realized. Furthermore, nuclear de-excitation lines can probe the propagation of low-energy cosmic rays in our Galaxy. In this presentation we will focus on the topics that can be addressed with long-lived stellar nucleosynthesis products, the intriguing open questions associated with Galactic positrons, and detection prospects in the next decade.