Testing the blast wave model with Swift GRBs

Abstract

The complex structure of the light curves of Swift GRBs (e.g. superimposed flares and shallow decay) has made their interpretationand that of the blast wave caused by the burst, more difficult than in the pre-Swift era. We aim to constrain the blast wave parameters:electron energy distribution, p, density profile of the circumburst medium, k, and the continued energy injection index, q. We do so bycomparing the observed multi-wavelength light curves and X-ray spectra of a Swift sample to the predictions of the blast wave model.We can successfully interpret all of the bursts in our multi-wavelength sample of 10, except two, within the framework of the blastwave model, and we can estimate with confidence the electron energy distribution index for 6 of the sample. Furthermore we identify jetbreaks in almost half of the bursts. The values of k suggest that the circumburst density profiles are not drawn from only one of theconstant density or wind-like media populations. A statistical analysis of the distribution of p reveals that, even in the most conservativecase of least scatter, the values are not consistent with a single, universal value. This is in agreement with our results for a larger sample ofX-ray only afterglows which we summarise here.