GeV-TeV and X-Ray Flares from Gamma-Ray Bursts

The recent detection of delayed X-ray flares during the afterglow phase of gamma-ray bursts suggests an inner engine origin, at radii inside the deceleration radius characterizing the beginning of the forward-shock afterglow emission. Given the observed temporal overlap between the flares and afterglows, there must be inverse Compton (IC) emission arising from such flare photons that are scattered by forward-shock afterglow electrons. We find that this IC emission produces GeV-TeV flares, which may be detected by GL AST and ground-based TeV telescopes. We speculate that this kind of emission may already have been detected by EGRET from a very strong burst—GRB 940217. The enhanced cooling of the forward-shock electrons by the X-ray flare photons may suppress the synchrotron emission of the afterglows during the flare period. The detection of GeV-TeV flares, combined with low-energy observations, may help to constrain the poorly known magnetic field in afterglow shocks. We also consider self-IC emission in the context of internal-shock and external-shock models for X-ray flares. The emission above GeV energies from internal shocks is low, while the external-shock model can also produce GeV-TeV flares, but with a different temporal behavior from that caused by IC scattering of flare photons by afterglow electrons. This suggests a useful approach for distinguishing whether X-ray flares originate from late central-engine activity or from external shocks.