Pulsars as the Sources of High Energy Cosmic Ray Positrons

TL;DR

This paper explores pulsars as a plausible source of high-energy cosmic ray positrons observed by PAMELA, suggesting they could explain the data without invoking dark matter, and discusses potential observational signatures.

Contribution

It demonstrates that pulsars can account for the PAMELA positron excess and proposes a method to distinguish pulsar sources from dark matter through anisotropy measurements.

Findings

Pulsars can produce the positron flux observed by PAMELA.

Nearby pulsars like Geminga significantly contribute to the spectrum.

Anisotropy measurements could differentiate pulsar and dark matter origins.

Abstract

Recent results from the PAMELA satellite indicate the presence of a large flux of positrons (relative to electrons) in the cosmic ray spectrum between approximately 10 and 100 GeV. As annihilating dark matter particles in many models are predicted to contribute to the cosmic ray positron spectrum in this energy range, a great deal of interest has resulted from this observation. Here, we consider pulsars (rapidly spinning, magnetized neutron stars) as an alternative source of this signal. After calculating the contribution to the cosmic ray positron and electron spectra from pulsars, we find that the spectrum observed by PAMELA could plausibly originate from such sources. In particular, a significant contribution is expected from the sum of all mature pulsars throughout the Milky Way, as well as from the most nearby mature pulsars (such as Geminga and B0656+14). The signal from nearby pulsars is expected to generate a small but significant dipole anisotropy in the cosmic ray electron spectrum, potentially providing a method by which the Fermi gamma-ray space telescope would be capable of discriminating between the pulsar and dark matter origins of the observed high energy positrons.