GeV emission from short gamma-ray bursts: the case of GRB 081024B

Abstract

We investigate whether the high energy tail detected by the Fermi/LAT for the short GRB 081024B can be caused by synchrotron and self-Compton emission in the context of either the internal or external shock models. For the internal shock scenario, we explore the possibility of generating the high energy photons directly by means of the synchrotron process, or inverse Compton emission in which target photons are synchrotron photons produced in internal shocks taking place in a lately emitted shell (delayed internal shocks). In the external shock scenario, we test whether the high energy tail can be an extension of the afterglow synchrotron emission, or alternatively the inverse Compton component associated with the afterglow synchrotron photons. For the internal shock scenario, we conclude that only an inverse Compton component from delayed internal shocks can explain the high energy tail that extends to the GeV range. In the external shock scenario, we show that the high energy tail may be interpreted as synchrotron afterglow emission, if the slow cooling phase starts as early as a few seconds after the trigger. On the other hand, the observed high energy tail is consistent with an inverse Compton component of the afterglow in the fast cooling regime.