Positron transport and annihilation in expanding flows: A model for the high-latitude annihilation feature

Abstract

Positron sources in the vicinity of the Galactic Center can account for the recently discovered high-latitude 0.511 MeV annihilation radiation if the positrons are convected away from the disk of the Galaxy and annihilate during transport. Here we describe our treatment for positron energy loss and thermalization, transport, and annihilation. The concept of the Maxwell-Boltzmann length (a generalized stopping distance) is outlined, and a model map of the distribution of annihilation radiation is presented for idealized flows.