The conspicuous gamma-ray burst of 30 May 1996
  The spectra of the majority of bursts exhibit a low-energy power law index, alpha, that is either a constant or becomes softer with time. However, in the burst of 30 May 1996 alpha becomes harder. Here we show that this behavior can be explained by a hybrid model consisting of a thermal and a non-thermal component. In this burst the power-law index of the non-thermal component changes drastically from s ~ -1.5 to s ~ -0.67 at approximately 5 seconds after the trigger, thereby revealing, at low energies, the thermal component with its hard Rayleigh-Jeans tail. This leads to the large alpha-values that are found if the Band function is fitted to the spectra. We suggest that the change in s could be due to a transition from fast to slow cooling of the electrons emitting in the BATSE range. This could be due to the fact that the magnetic field strength becomes weaker. 
Felix Ryde, Milan Battelino (Stockholm University)