P. Schady
Prompt Observations Of Gamma-Ray Bursts with Swift
2007 (Supervisor: K. O. Mason)

This thesis uses early-time and simultaneous data from all three instruments on-board Swift to explore how the conditions of long Gamma-Ray Bursts (GRBs) and their environment affect their observed prompt and afterglow properties.

I firstly analyse two long GRBs with properties that distinguish them from the more standard class of long GRB; XRF 050406 and GRB 061007. The X-Ray Flash XRF 050406 is a class of GRB with softer prompt emission spectra than is typically observed. At the time, Swift UVOT observations of XRF 050406 were the earliest to be taken of an XRF optical counterpart, and the temporal and spectral Swift multi-wavelength data indicate that the bursts' softness is due to a geometrical effect where the GRB is observed off-axis. GRB 061007 is the brightest GRB to be detected by Swift and is accompanied by an exceptionally luminous afterglow that had a V-band magnitude < 11.1 at 80 s after the prompt emission. Although several properties of GRB 061007 are comparable to that of more standard GRBs, the brightness and the similarity in the decay rate of the X-ray, UV/optical and γ-ray emission from 100 s after the trigger require either an excessively large kinetic energy or highly collimated outflow.

To study GRB local environments, I analyse the X-ray and UV/optical spectral energy distributions of seven GRBs, and determine the column density and dust extinction in the GRB local environment. Using the SMC, LMC and Milky Way extinction curves to model the host galaxy dust, I find the SMC model to provide the best fit to the majority of the sample, indicating that the local environments of long GRBs are characteristic of irregular, low metallicity galaxies. I investigate the factors that contribute to the extinction and absorption in GRB afterglows, and the implications for the host galaxy properties.