Narrow Results

It is shown that the concept of a fireball with a definite filamentary structure naturally emerges from the analysis of the spectra of Gamma-Ray Bursts (GRBs). These results, made possible by the recently obtained analytic expressions of the equitemporal surfaces in the GRB afterglow, depend crucially on the single parameter ℛ describing the effective area of the fireball emitting the X-ray and gamma-ray radiation. The X-ray and gamma-ray components of the afterglow radiation are shown to have a thermal spectrum in the co-moving frame of the fireball and originate from a stable shock front described self-consistently by the Rankine–Hugoniot equations. Precise predictions are presented on a correlation between spectral changes and intensity variations in the prompt radiation verifiable, e.g., by the Swift and future missions. The highly variable optical and radio emission depends instead on the parameters of the surrounding medium. The GRB 991216 is used as a prototype for this model.

We analyze GRB060607A within the fireshell model. The temporal properties of the flares observed in the decaying phase of the X-ray afterglow are reproduced by the same mechanism than the prompt emission light curve: the interaction of the optically thin fireshell with overdense CircumBurst Medium (CBM) clumps. The main observational differences between these two regimes depend on the typical dimensions of the clumps with respect to the visible area of the fireshell.