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Abstract: We perform a detailed study of inverse Compton (IC) emission for a fireballundergoing external shock (ES) in either a uniform or a wind-like interstellarmedium, and assess the relative importance of IC and synchrotron emissions. Wedetermine the primary model parameters driving the IC to synchrotron emissionratio in the case of a short duration central engine. We then investigate thecase of ES by a long duration central engine, or delayed external shock (DES),a model that can account for some of the flares observed in GRB X-ray lightcurves. We present model predictions, in particular in terms of GeV vs X-raybehavior, and compare them with other models proposed to explain the origin offlares. We find that if most of the emission occurs when the fireball is in thefast cooling regime, then a substantial GeV emission is expected both for ashort (standard ES) and a long (DES) duration central engine activity. Inparticular, in the context of standard ES we are able to account for thedelayed emission observed in GRB940217. In the case of DES, we find that ICscattering of X-ray flare photons can produce high energy flares in the GeVband, which can be detected by GLAST. The detectability of high energy flaresimproves with the burst kinetic energy: about 30% of Swift GRBs showing flaresin their X-ray light curve have sufficiently large kinetic energy so that theexpected high flares can be detected by GLAST. One important prediction of theDES model is the simultaneity between low and high energy flares. To test thissimultaneity, the peak energies of both flares need to fall below or within theobservational bands. We predict that X-ray flares with peak energy of ~10 eVproduce high energy flares with peak energy of around 100 MeV-GeV. Observationsby Swift and GLAST then, can test the predicted simultaneity.



Author: A. Galli (1,2,3), L. Piro (1) ((1) IASF-Roma-INAF, (2) Univerisita' di Roma La Sapienza, (3) INFN-Trieste)

Source: https://arxiv.org/



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