On the Contribution of Pulsars to the Positron Fraction in Cosmic Rays

TL;DR

This paper investigates whether pulsars like Vela and Crab can explain the observed positron excess in cosmic rays, but finds their contribution insufficient to match experimental data from PAMELA and AMS.

Contribution

It provides a detailed analysis of pulsar contributions to cosmic ray positrons using diffusion models, challenging the idea that pulsars alone account for the positron excess.

Findings

Pulsar-origin positron spectra do not match the observed excess.

Diffusion model results show inconsistency with experimental positron ratios.

Pulsars alone are unlikely to explain the positron excess in cosmic rays.

Abstract

Several cosmic ray experiments have measured the positron fraction up to few hundred GeV. Their data have revealed an excess of positrons above 10 GeV that is not consistent with the secondary production of these particles in the interstellar medium. A primary source like dark matter or astrophysical sources (e.g pulsars and their nebulae) were considered to account for such an excess. In this paper we analyse the possibility of a primary positron production due to pulsars. Under the assumption of equal initial spectra at the source for positrons, electrons, and gamma-rays we study the propagation of particle spectra using a diffusion model in the Galaxy. We focused our analysis on the Vela and Crab pulsars and their associated nebulae, which are well observed in gamma-rays. Comparison with experimental data is reported. The propagated positron and electron spectra generated from these sources result in a positron ratio, which is largely inconsistent with the excess observed by PAMELA and AMS