Early photon-shock interaction in stellar wind: sub-GeV photon flash and high energy neutrino emission from long GRBs
Abstract
For gamma-ray bursts (GRBs) born in a stellar wind, as the reverse shock crosses the ejecta, usually the shocked regions are still precipitated by the prompt MeV \gamma-ray emission. Because of the tight overlapping of the MeV photon flow with the shocked regions, the optical depth for the GeV photons produced in the shocks is very large. These high energy photons are absorbed by the MeV photon flow and generate relativistic e^\pm pairs, which re-scatter the prompt $\gamma-$rays and power detectable sub-GeV emission. Since the total energy contained in the forward shock region and the reverse shock region are comparable, the predicted sub-GeV emission is independent on whether the GRB ejecta are magnetized (in which case the reverse shock IC and synchrotron self-Compton emission is suppressed). As a result, sub-GeV flashes are generic for the GRB wind model, and they should be typically detectable by the future {\em Gamma-Ray Large Area Telescope}. Overlapping also influence neutrino emission. Besides the 10^{15} \sim 10^{17} eV neutrino emission powered by the interaction of the shock accelerated protons with the synchrotron photons in both the forward and reverse shock regions, there comes another 10^{14} eV neutrino emission component powered by protons interacting with the MeV photon flow. This last component has a similar spectrum to the one generated in the internal shock phase, but the typical energy is slightly lower.Keywords
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