5 Short timescale variability of prompt and delayed GRB emissions

One of the central problems in GRB studies is to explain the diversity of GRB time profiles. We argued above that the simple FRED-type profiles can be understood by blast wave deceleration in a uniform or smoothly varying CBM where the density $n(x)\propto x^{-\eta}$.To explain the temporal variability of GRBs, we (Dermer & Mitman 1999) recently considered a highly-structured cloudy medium on a large range of distance scales. Column densities of only 10¹⁶-10²⁰ cm^-2 are needed to efficiently extract the energy from a relativistic blast wave, so the properties of such a CBM medium are not extreme. A CBM that is inhomogeneous on small scales also breaks the symmetry on angular scales $\ll 1/\Gamma_0$, so that the objections of Fenimore and colleagues are met regarding emission from a single relativistic shell (Fenimore et al. 1996).