Annihilation Radiation in the Galaxy

TL;DR

This paper reviews observations and mechanisms of galactic annihilation radiation, discussing positron production, physical processes, spectral calculations, and implications for mapping annihilation sites with INTEGRAL.

Contribution

It provides a comprehensive overview of astrophysical sources, processes, and spectral modeling of galactic annihilation radiation, including recent estimates and the role of compact objects.

Findings

Positron production rates from nova and supernova nucleosynthesis are summarized.

Spectral calculations show how different media affect annihilation signatures.

High-temperature plasmas and dust can quench positronium, influencing observed spectra.

Abstract

Observations of annihilation radiation in the Galaxy are briefly reviewed. We summarize astrophysical mechanisms leading to positron production, and recent estimates for production rates from nova and supernova nucleosynthesis in the Galaxy. The physical processes involved in the production of annihilation radiation in the interstellar medium are described. These include positron thermalization, charge exchange, radiative recombination, and direct annihilation. Calculations of 2\gamma and 3\gamma spectra and the positronium (Ps) fraction due to the annihilation of positrons in media containing H and He at different temperatures and ionization states are presented. Quenching of Ps by high temperature plasmas or dust could account for differences between 0.511 MeV and 3\gamma Ps continuum maps. These results are presented in the context of the potential of INTEGRAL to map sites of annihilation radiation in the Galaxy. Positron production by compact objects is also considered.