Ultra-high Energy Cosmic Rays and Neutron-Decay Halos from Gamma Ray Bursts

Abstract.

Simple arguments concerning power and acceleration effciency show that ultra-high energy cosmic rays (UHECRS) with energies $\gtrsim 10^{19}$ eV could originate from GRBs. Neutrons formed through photo-pion production processes in GRB blast waves leave the acceleration site and travel through intergalactic space, where they decay and inject a very energetic proton and electron component into intergalactic space. The neutron-decay protons form a component of the UHECRs, whereas the neutron-decay electrons produce optical/X-ray synchrotron and gamma radiation from Compton-scattered background radiation. A significant fraction of galaxies with GRB activity should be surrounded by neutron-decay halos of characteristic size $\sim 100$ kpc.