Prompt GeV emission in the synchrotron self-Compton model for Gamma-Ray Bursts

The detection in 10 bursts of an optical counterpart emission (i.e. during the prompt GRB phase) that is 10−104 brighter than the extrapolation of the burst spectrum to optical frequencies suggests a synchrotron self-Compton origin for the GRB emission, synchrotron producing the optical counterpart emission. In this model, the second upscattering of the burst photons yields a prompt GeV–TeV emission, whose brightness depends strongly on an unknown quantity, the peak energy of the primary synchrotron spectrum. Measurements of the optical, γ-ray, and GeV prompt fluxes can be used to test the synchrotron self-Compton model for GRBs and to determine directly the total radiative output of GRBs. For a set of 29 GRBs with optical counterpart detections, we find that the expected GeV photon flux should correlate with the fluence of the sub-MeV emission and anticorrelate with the brightness of the optical counterpart, the strength of these correlations decreasing for an increasing width of the synchrotron peak energy distribution. The detection of a GeV prompt emission consistent with the extrapolation of the burst spectrum to higher energies would rule out the synchrotron selfCompton model if the sub-MeV burst emission were very bright and the (intrinsic) optical counterpart