The Double-Peak Spectral Energy Density of Gamma-Ray Bursts and the True Identity of GRB 031203

Abstract

A double-peak spectral energy density of prompt γ-rays, similar to that observed in blazars, is expected in the cannonball (CB) model of gamma-ray bursts (GRBs) produced in supernova (SN) explosions. The first sub-MeV ordinary peak is formed by inverse Compton scattering (ICS) of the ambient SN light by the CBs' electrons, while the second peak at GeV-TeV energies is formed by ICS of interstellar medium electrons accelerated by the jetted CBs from the SN explosion. Usually the second peak is in the GeV-TeV range. However, in X-ray flashes with a low peak energy, which in the CB model are normal GRBs viewed far off-axis, the second peak energy moves to the MeV range. In far off-axis GRBs, such as 980425 and 031203, the second peak may have been confused with the normal GRB peak. In most GRBs that have been observed so far, the γ-ray detectors ran out of statistics far below the second peak. However, in bright GRBs, the two peaks may be resolved by simultaneous measurements with Swift, INTEGRAL, and GLAST.