Origin of delayed GeV emission from gamma-ray bursts within stellar clusters
August 16, 2017
August 03, 2018
A significant part of long Gamma-ray Bursts (GRBs) shows delayed hard GeV gamma-ray emission in addition to the dominant emission observed in the keV-MeV energy range. We argue that such emission can appear when the anisotropic explosion of a massive star occurs in a dense stellar cluster. Then, the delayed GeV gamma-rays can be produced when the hyper-relativistic jet encounters the radiation of stars, within the stellar cluster, which happens to be
immersed in the jet. The hard X-ray to soft gamma-ray radiation from the jet, heats the surfaces of encountered stars to temperatures above those expected from nuclear burning. Then, relativistic electrons in the jet can efficiently Inverse Compton up-scatter stellar radiation to the GeV energies. We have performed numerical calculations of the gamma-ray spectra produced in the IC pair cascade initiated by relativistic electrons in a dense stellar radiation field. The gamma-ray spectra produced in such scenario form additional component in the GRB spectrum which is delayed in respect to the main emission, coming from the central part of the GRB engine, since stars can be encountered up to a parsec distance scale from the GRB. Such mechanism is discussed for the delayed GeV emission recently observed from the powerful GRB 130427A.
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