AMIRI , M.

It has recently become clear that in both short and long gamma-ray bursts (GRBs) it coexists a sequence of different events, each characterized by specific physical processes and corresponding values of the Lorentz gamma factors. The ultra-relativistic prompt emission (UPE) phase, with Lorentz factor $\Gamma\leq10^4$, is followed by a mildly...

We address the significance of the observed GeV emission from \textit{Fermi}-LAT on the understanding of the structure of long GRBs. We examine 82 X-ray Flashs (XRFs), in none of them GeV radiation is observed, adding evidence to the absence of a black hole (BH) formation in their merging process. By examining $329$ Binary-driven Hypernovae...