Heating and deceleration of GRB fireballs by neutron decay
  Fireballs with high energy per baryon rest mass (> 400) contain a relatively slow neutron component. We show here that in this situation the thermal history of fireballs is very different from the standard adiabatic cooling. 
Elena M. Rossi (IoA, Cambridge), Andrei M. Beloborodov (Columbia   University) and Martin J. Rees (IoA, Cambridge)