Compton dragged gamma-ray bursts: the spectrum
  We calculate the spectrum resulting from the interaction of a fireball with ambient soft photons. These photons are assumed to be produced by the walls of a funnel in a massive star. By parameterizing the radial dependence of the funnel temperature we calculate the deceleration of the fireball self-consistently, taking into account the absorption of high energy gamma-rays due to interaction with the softer ambient photons. The resulting spectrum is peaked at energies in agreement with observations, has a nu^2 slope in the X-ray band and a steep power-law high energy tail. 
G. Ghisellini, D. Lazzati (Osserv. Astr. di Brera), A. Celotti (Sissa,   Trieste), M.J. Rees (IoA Cambridge)