GRB 030226 in a Density-Jump Medium

We present an explanation for the unusual temporal feature of the gamma-ray burst GRB 030226 afterglow. The R -band afterglow of this burst faded as ~ t -1.2 ~0.2 days after the burst, rebrightened during the period of ~0.2-0.5 days, and then declined with ~ t -2.0 . To fit such a light curve, we consider an ultrarelativistic jetted blast wave expanding in a density-jump medium. The interaction of the blast wave with a large density jump produces relativistic reverse and forward shocks. In this model, the observed rebrightening is due to emissions from these newly forming shocks, and the late-time afterglow is caused by the sideways expansion of the jet. Our fitting implies that the progenitor star of GRB 030226 could have produced a stellar wind with a large density jump prior to the GRB onset.