Intrinsic Parameters of GRB990123 from Its Prompt Optical Flash and Afterglow

Abstract

We have constrained the intrinsic parameters, such as the magnetic energy density fraction ($ε_{B}$), the electron energy density fraction ($ε_e$), the initial Lorentz factor ($Γ_0$) and the Lorentz factor of the reverse external shock ($Γ_{rs}$), of GRB990123, in terms of the afterglow information (forward shock model) and the optical flash information (reverse shock model). Our result shows: 1) the inferred values of $ε_e$ and $ε_B$ are consistent with the suggestion that they may be universal parameters, comparing to those inferred for GRB970508; 2) the reverse external shock may have become relativistic before it passed through the ejecta shell. Other instrinsic parameters of GRB990123, such as energy contained in the forward shock $E$ and the ambient density $n$ are also determined and discussed in this paper.