  When a cold shell sweeps up the ambient medium, a forward shock and a reverse
shock will form. We analyze the reverse-forward shocks in a wind environment,
including their dynamics and emission. An early afterglow is emitted from the
shocked shell, e.g., an optical flash may emerge. The reverse shock behaves
differently in two approximations: relativistic and Newtonian cases, which
depend on the parameters, e.g., the initial Lorentz factor of the ejecta. If
the initial Lorentz factor is much less than $114 E_{53}^{1/4}
\Delta_{0,12}^{-1/4} A_{*,-1}^{-1/4}$, the early reverse shock is Newtonian.
This may take place for the wider of a two-component jet, an orphan afterglow
caused by a low initial Lorentz factor, and so on. The synchrotron self
absorption effect is significant especially for the Newtonian reverse shock
case, since the absorption frequency $\nu_a$ is larger than the cooling
frequency $\nu_c$ and the minimum synchrotron frequency $\nu_m$ for typical
parameters. For the optical to X-ray band, the flux is nearly unchanged with
time during the early period, which may be a diagnostic for the low initial
Lorentz factor of the ejecta in a wind environment. We also investigate the
early light curves with different wind densities, and compare them with these
in the ISM model.
