Modeling the optical afterglow of GRB 030329

Abstract

The best-sampled afterglow light curves available are for GRB 030329. A distinguishing feature of this event is the obvious rebrightening at around 1.6 days after the burst. Proposed explanations for the rebrightening mainly include the two-component jet model and the refreshed-shock model, although a sudden density jump in the circumburst environment is also a potential choice. Here we reexamine the optical afterglow of GRB 030329 numerically in light of the three models. In the density-jump model, no obvious rebrightening can be produced at the jump moment. In addition, after the density jump, the predicted flux density decreases rapidly to a level that is significantly below observations. A simple density-jump model thus can be excluded. In the two-component jet model, although the observed late afterglow (after 1.6 days) can potentially be explained as emission from the wide component, the emergence of this emission actually is too slow, and it does not manifest as a rebrightening as previously expected. The energy-injection model seems to be the most preferred choice. By engaging a sequence of energy-injection events, it provides an acceptable fit to the rebrightening at ∼1.6 days, as well as the whole observed light curve that extends to ~80 days. Further studies on these multiple energy-injection processes may provide a valuable insight into the nature of the central engines of gamma-ray bursts. © 2006. The American Astronomical Society. All rights reserved.