GRB050525A: Multiband modelling of the afterglow

摘要

The Swift era has posed a challenge to the standard blast-wave model of Gamma Ray Burst afterglows. The achromatic steepening of the afterglow lightcurves ('jet break') considered in the model as the signature of outflow collimation, has become almost rare. Several afterglows exhibited complex lightcurves that did not confirm by the predicted spectral - temporal 'closure relations' of the blastwave model. Here we present optical observations and broadband modelling of the afterglow of GRB0505025A, a bright burst detected and followed up by Swift. We find that the overall evolution of the afterglow can not be explained by a single forward shock emission, though the late time evolution is compatible with the predictions of the standard afterglow model, including a jet break. We explain the afterglow evolution based on a two-component jet model and estimate the physical parameters.