External Shocks, UHECRs, and the Early Afterglow of GRBs
  Highly variable gamma-ray pulses and X-ray flares in GRB light curves can result from external shocks rather than central engine activity under the assumption that the GRB blast-wave shell does not spread. Acceleration of cosmic rays to 10^{20} eV energies can take place in the external shocks of GRBs. Escape of hadronic energy in the form of UHECRs leads to a rapidly decelerating GRB blast wave, which may account for the rapid X-ray declines observed in Swift GRBs. 
Charles D. Dermer (NRL)