A Gamma-Ray Burst/Pulsar for Cosmic-Ray Positrons with a Dark Matter-like Spectrum

TL;DR

This paper suggests that a nearby ancient gamma-ray burst or pulsar could explain the observed excesses of cosmic-ray positrons and electrons, with spectral features similar to dark matter predictions, and proposes methods to distinguish their origins.

Contribution

It introduces an astrophysical model involving a past gamma-ray burst or pulsar to explain cosmic-ray excesses, offering testable predictions to differentiate from dark matter.

Findings

Reproduces observed cosmic-ray spectra with an astrophysical source.

Predicts spectral cutoff and anisotropy signatures for source identification.

Provides a framework to distinguish astrophysical sources from dark matter.

Abstract

We propose that a nearby gamma-ray burst (GRB) or GRB-like (old, single and short-lived) pulsar/supernova remnant/microquasar about 10^{5-6} years ago may be responsible for the excesses of cosmic-ray positrons and electrons recently observed by the PAMELA, ATIC/PPB-BETS, Fermi and HESS experiments. We can reproduce the smooth Fermi/HESS spectra as well as the spiky ATIC/PPB-BETS spectra. The spectra have a sharp cutoff that is similar to the dark matter predictions, sometimes together with a line (not similar), since higher energy cosmic-rays cool faster where the cutoff/line energy marks the source age. A GRB-like astrophysical source is expected to have a small but finite spread in the cutoff/line as well as anisotropy in the cosmic-ray and diffuse gamma-ray flux, providing a method for the Fermi and future CALET experiments to discriminate between dark matter and astrophysical origins.