Double-peak spectral energy density of GRBs and the true identity of GRB 031203

Abstract

A double-peak spectral-energy-density of gamma-rays, similar to that observed in blazars, is expected in gamma-ray bursts (GRBs) produced in supernova (SN) explosions. The second peak, which is formed by inverse Compton scattering of ambient SN light by cosmic ray electrons accelerated by the jets from the SN explosion, has a much higher peak-energy than the first ordinary peak. However, in X-ray flashes (XRFs), which in the cannonball (CB) model are normal GRBs viewed farther off axis, the first peak-energy is shifted to the soft X-ray region while the second peak-energy moves to the MeV range. In far-off-axis GRBs, such as GRBs 980425 and 031203, the second peak may have been confused with the normal GRB peak. In most GRBs, which have been observed so far, the gamma-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 and GLAST.Comment: The estimated soft X-ray fluence in GRB 031203 was replaced in the text and Fig. 3 with the correct estimate by Vaughan et al. Corrected typo