2012MNRAS.427..288R

The Swift era has posed a challenge to the standard blast-wave model of gamma-ray burst (GRB) afterglows. The key observational features expected within the model are rarely observed, such as the achromatic steepening (`jet break') of light curves. The observed afterglow light curves showcase additional complex features requiring modifications within the standard model. Here we present optical/near-infrared observations, millimetre upper limits and comprehensive broad-band modelling of the afterglow of the bright GRB 0505025A, detected by Swift. This afterglow cannot be explained by the simplistic form of the standard blast-wave model. We attempt modelling multiwavelength light curves using (i) a forward–reverse shock model, (ii) a two-component outflow model and (iii) a blast-wave model with a wind termination shock. The forward–reverse shock model cannot explain the evolution of the afterglow. The two-component model is able to explain the average behaviour of the afterglow very well but cannot reproduce the fluctuations in the early X-ray light curve. The wind termination shock model reproduces the early light curves well but deviates from the global behaviour of the late-time afterglow.