2000MNRAS.319.1159W

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 (Γ₀) and the Lorentz factor of the reverse external shock (Γ_rs), of GRB 990123, 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 GRB 970508; (2) the reverse external shock may have become relativistic before it passed through the ejecta shell. Other intrinsic parameters of GRB 990123, such as the energy contained in the forward shock E and the ambient density n, are also determined and discussed in this paper.