Positron production scenarios and the angular profile of the galactic center 511-keV line

TL;DR

This paper investigates various dark matter and positron production models to explain the angular profile of the 511-keV line from the galactic center, considering effects like positron migration and transient events.

Contribution

It compares different positron production scenarios and dark matter distributions to match the observed angular profile, highlighting the roles of positron diffusion and transient events.

Findings

Relic decay scenarios produce too flat an angular profile.

Dark matter-dark matter collisions can match observations with suitable distributions.

Positron migration over half a kiloparsec is inconsistent with most dark matter models.

Abstract

The observed angular profile of the 511-keV photon excess from the Milky Way galactic center can allow us to select among combinations of various dark matter and other positron production mechanisms with various models for the dark matter distribution. We find that a relic decay scenario gives too flat an angular distribution for any dark matter distribution in our survey, but that a dark matter-dark matter collisional scenario, or a scenario that involves particles emitted from a localized central source producing positrons some distance out, can match the observed galactic center angular profile if the dark matter distribution is neither too flat nor too cuspy. Additionally, positron migration or diffusion before annihilation broadens the angular profile to an extent that an average migration of more than half a kiloparsec is not viable with most dark matter distributions. The observed angular profile is also consistent with the occurrence of transient events in the past, followed by isotropic positron diffusion.