Nanjing Univ, Dept Astron, Nanjing 210093, Peoples R China
; CCAST, World Lab, Beijing 100080, Peoples R China
; CAS, IHEP, LCRHEA, Beijing 100039, Peoples R China
The conventional generic model is considered to explain the dynamics of gamma-ray burst remnants very well, no matter whether they are adiabatic or highly radiative. However, we find that, for adiabatic expansion, the model cannot reproduce the Sedov solution in the nonrelativistic phase, and thus it needs to be revised. In this paper a new differential equation is derived. The generic model based on this equation is shown to be correct for both radiative and adiabatic fireballs, and in both ultrarelativistic and non-relativistic phases.