DELAYED GEV-TEV PHOTONS FROM GAMMA-RAY BURSTS PRODUCING HIGH-ENERGY COSMIC-RAYS

A scenario in which cosmic rays (CRs) above 10(20) eV are produced by cosmological gamma-ray bursts (GRBs) is consistent with observations, provided that deflections by the intergalactic magnetic field (IGMF) d elay and spread the arrival time of the CRs over greater than or equal to 50 yr. The energy lost by the CRs as they propagate and interact w ith the microwave background is transformed by cascading into secondar y GeV-TeV photons. We show that a significant fraction of these photon s can arrive with delays much smaller than the CR delay if much of int ergalactic space is occupied by large-scale magnetic ''voids,'' region s of a size greater than or similar to 5 Mpc and a field weaker than 1 0(-15) G. Such voids might be expected, for example, in models where a weak primordial field is amplified in shocked, turbulent regions of t he intergalactic medium during the formation of large-scale structure. For a field strength similar to 4 x 10(-11) G in the high-field regio ns, the value required to account for observed galactic fields if the IGMF were frozen in the protogalactic plasma, the delay of CRs produce d by a burst at a distance of 100 Mpc is similar to 100 yr, and the fl uence of secondary photons above 10 GeV on hour-day timescales is I(>E ) similar to 10(-6) E(TeV)(-1) cm(-2). This fluence is close to the de tection threshold of current high-energy gamma-ray experiments. Detect ion of the delayed flux would support the GRB-CR association and would also provide information on the IGMF structure.