On the 511 keV emission line of positron annihilation in the Milky Way

TL;DR

This paper reviews the sources and propagation of positrons in the Milky Way, suggesting many positrons escape the disk and may annihilate in the bulge, affecting interpretations of the 511 keV emission line observations.

Contribution

It proposes that positrons from the disk propagate into the bulge via magnetic fields, offering a new perspective on the origin of the 511 keV line.

Findings

Most disk positrons escape detection due to low surface brightness.

Positrons may be transported into the bulge along magnetic field lines.

This transport could explain the observed annihilation emission distribution.

Abstract

I review our current understanding of positron sources in the Galaxy, on the basis of the reported properties of the observed 511 keV annihilation line. It is argued here that most of the disk positrons propagate away from the disk and the resulting low surface brightness annihilation emission is currently undetectable by SPI/INTEGRAL. It is also argued that a large fraction of the disk positrons may be transported via the regular magnetic field of the Galaxy into the bulge and annihilate there. These ideas may alleviate current difficulties in interepreting INTEGRAL results in a "conventional" framework.