The Ep distribution of long-duration γ-ray bursts observed by the PHEBUS experiment

Abstract

We present a distribution in E p, the break energy of γ-ray burst (GRB) spectra, obtained from a spectral analysis of 91 long-duration, high fluence, GRBs recorded by the PHEBUS experiment. From spectral fits above 0.1 MeV of 279 time slices during these 91 GRB events, the centroid of the E p distribution is found to be ∼0.41 MeV while the full width at half maximum (FWHM) is ∼0.60 MeV. These values are significantly higher than those derived from BATSE data (viz. ∼0.25 and ∼0.30 MeV, respectively). Nevertheless, we confirm that the E p distribution is narrow with an upper-energy limit at about 2 MeV.