A Gamma-ray Burst/pulsar for Cosmic-ray Positrons with a Dark Matter-like Spectrum

We propose that a nearby gamma-ray burst (GRB) or GRB-like (old, single and short-lived) pulsar/microquasar about 105−6 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. Subject headings: cosmic rays — diffusion — gamma rays: bursts — gamma rays: theory — pulsars: general — radiation mechanism: non-thermal