Can Ultrahigh Energy Cosmic Rays Come from Gamma-Ray Bursts? II: Cosmic Rays Below the Ankle and Galactic GRB

TL;DR

This paper demonstrates that long gamma-ray bursts in the interstellar medium can accelerate cosmic rays up to the ankle energy (~4×10^{18} eV), but extragalactic GRBs likely cannot account for cosmic rays above this energy without conflicting with observational limits.

Contribution

It derives the maximum energy cosmic rays can attain from relativistic blast waves of long GRBs and discusses the implications for Galactic and extragalactic cosmic-ray origins.

Findings

Galactic GRB shocks can produce cosmic rays up to the ankle energy.

Extragalactic GRBs are unlikely to account for cosmic rays above the ankle without violating flux limits.

Intermittency and beaming reduce the contribution of Galactic GRBs to observed cosmic rays.

Abstract

The maximum cosmic ray energy achievable by acceleration by a relativistic blast wave is derived. It is shown that forward shocks from long GRB in the interstellar medium are powerful enough to produce the Galactic cosmic-ray component up to the ankle at $4\times 10^{18}$eV, as per an earlier suggestion (Levinson and Eichler, 1993). It is further argued that, were extragalactic long GRB responsible for the component {\it above} the ankle as well, the contribution from an occasional Galactic GRB within the solar circle would yield more than the observational limits on the outward flux from the solar circle, unless intermittency and/or beaming causes the present-day contribution to be less than $10^{-3}$ times the time average, and difficulties with these avoidance scenarios are also noted.