Modelling the prompt and afterglow emission of gamma-ray bursts

This thesis studies the broadband behaviour of GRBs by fitting a detailed spectral/temporal model to both the prompt and afterglow hard and soft X-ray emission observed by the Swift satellite. The prompt emission is decomposed into pulses which are fitted individually while the afterglow is modelled using a smoothly varying broad pulse which evolves into a power-law decay at late times. Using this model a comprehensive study of GRB 080310 is presented and followed by similar analyses of GRB 061121, GRB 080810 and GRB 081008. The optical behaviour is found to be inconsistent with the high-energy model: a spectral break between the X-ray and optical band is necessary and for many prompt pulses the self-absorption mechanism is required. The latter three bursts have optical afterglows that are shown to be inconsistent with those fitted to the X-ray regime, peaking earlier in the lower energy bands and requiring a low-energy spectral break. The prompt optical emission seen from GRB 061121 has pulse-like features which match reasonably well with contemporaneous high-energy features, but have longer durations. The same model was used to study the expected evolution of GRB properties when moved to higher redshifts. Using a sample of bright Swift GRBs, the changes in measured duration with redshift were found to be driven by a combination of time dilation, gradual loss of pulse tails and sudden loss of pulses as the flux falls below instrumental sensitivity. A realistic sample of synthetic bursts is produced which, when simulated at high redshift, are found to be significantly longer in duration that the observed high redshift GRBs. Also demonstrated is that several bright bursts seen by Swift could be detected if they occurred at a redshift > 10 encouraging the use of GRBs as probes of the early Universe.