Extinct radio pulsars as a source of subrelativistic positrons

TL;DR

This paper proposes that extinct radio pulsars could be a significant source of subrelativistic positrons in the Galaxy, potentially explaining the observed 511-keV annihilation line.

Contribution

It introduces a model where old neutron stars produce positrons via gamma-ray absorption, linking extinct pulsars to Galactic positron excess.

Findings

Positron flux from old neutron stars is estimated at ~3 x 10^{43} s^{-1}.

Positron energies are below 10 MeV, consistent with observations.

Model aligns with requirements for the 511-keV Galactic annihilation line.

Abstract

Extinct radio pulsars, in which stationary, self-sustaining generation of a relativistic electron-positron plasma becomes impossible when rotation brakes down, can be sources of a subrelativistic flux of positrons and electrons. We assume that the observed excess of positrons in the bulge and the disc of the Galaxy is associated with these old neutron stars. The production of pairs in their magnetospheres occurs due to one-photon absorption of gamma quanta of the Galactic and extragalactic backgrounds. The cascade process of plasma production leads to the flux of positrons escaping from the open magnetosphere $\simeq 3 \times 10^{34} \text{ s}^{-1}$. The total flux of positrons from all old Galactic neutron stars with rotational periods $1.5 < P < 35$ s is $\simeq 3 \times 10^{43} \text{ s}^{-1}$. The energy of positrons is less than $\simeq 10$ MeV. The estimated characteristics satisfy the requirements for the positron source responsible for the 511-keV Galactic annihilation line.