Modeling the Optical Afterglow of GRB 030329

The best-sampled afterglow light curves are available for GRB 030329. Adistinguishing feature of this event is the obvious rebrightening at around 1.6days after the burst. Proposed explanations for the rebrightening mainlyinclude the two-component jet model and the refreshed shock model, although asudden density-jump in the circumburst environment is also a potential choice.Here we re-examine the optical afterglow of GRB 030329 numerically in light ofthe three models. In the density-jump model, no obvious rebrightening can beproduced at the jump moment. Additionally, after the density jump, thepredicted flux density decreases rapidly to a level that is significantly belowobservations. A simple density-jump model thus can be excluded. In thetwo-component jet model, although the observed late afterglow (after 1.6 days)can potentially be explained as emission from the wide-component, the emergenceof this emission actually is too slow and it does not manifest as arebrightening as previously expected. The energy-injection model seems to bethe most preferred choice. By engaging a sequence of energy-injection events,it provides an acceptable fit to the rebrightening at $\sim 1.6$ d, as well asthe whole observed light curve that extends to $\sim 80$ d. Further studies onthese multiple energy-injection processes may provide a valuable insight intothe nature of the central engines of gamma-ray bursts.Comment: 18 pages, 3 figures; a few references added and minor word changes; now accepted for publication in Ap