HIGH-ENERGY GAMMA-RAYS FROM ULTRA-HIGH-ENERGY COSMIC-RAY PROTONS IN GAMMA-RAY BURSTS

It has recently been proposed that ultra-high-energy (greater than or equal to 10(19) eV) cosmic rays (UHECRs) are accelerated by the blast waves associated with GRBs. We calculate the observed synchrotron spec trum from protons and energetic leptons formed in the cascades initiat ed by photopion production, taking into account gamma gamma attenuatio n at the source. Normalizing to the emission characteristics of GRB 97 0508,we predict similar to 10 MeV-100 GeV fluxes at a level that may h ave been observed with EGRET from bright GRBs and could be detected wi th the proposed GLAST experiment or with ground-based air Cerenkov tel escopes having thresholds less than or equal to several hundred GeV. T he temporal decay of the UHECR-induced high-energy gamma-ray afterglow s is significantly slower than that of the lower energy burst and asso ciated synchrotron self-Compton (SSC) radiation, which provides a dire ct way to test the hadronic origin of a high-energy GRB afterglow. Bes ides testing the UHECR origin hypothesis, the short-wavelength emissio n and afterglows can be used to probe the level of the diffuse interga lactic infrared radiation field or constrain redshifts of GRB sources.