A gamma-ray burst/pulsar for cosmic ray positrons with a dark matter-like spectrum

Abstract

We propose that a nearby gamma-ray burst (GRB) or GRB-like (old, single, and short-lived) pulsar, supernova remnant, or microquasar about 10 5-6 years ago may be responsible for the excesses of cosmic ray positrons and electrons recently observed in 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 high-energy cosmic rays cool fast 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.