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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 axe comparable to that of more standard GRBs, the brightness and the similarity in the decay rate of the X-ray, UV/optical and 7-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.

Short gamma-ray bursts (SGRBs) are extremely bright flashes of gamma-rays, lasting less than 2 s, originating from beyond the Milky Way but their progenitors remain unknown. The most popular progenitor theory involves the merger of two compact objects, either two neutron stars (NSs) or a NS and a black hole (BH), which then collapse to form a BH. A small proportion of SGRBs may instead be giant flares from extragalactic soft gamma-ray repeaters (SGRs) in nearby galaxies. The aim of this Thesis is to place constraints on the progenitors of SGRBs using multiwavelength observational data. The extragalactic SGR giant flare theory is tested by considering the properties of three candidate SGRBs which may have occurred in nearby host galaxies. It is likely that only one of the three was an extragalactic SGR giant flare and, although they are all shown to be consistent with this progenitor, GRB 070201 is most convincing candidate. Afterglow predictions are made for future candidates. Following on from the giant flare candidates, more typical SGRBs are considered. GRB 080905A is the nearest confirmed SGRB, occurring offset from a spiral galaxy at z∼0.12 which is studied using spatially resolved spectroscopy. The properties of GRB 080905A are shown to be consistent with a compact binary merger. GRB 090515 was a SGRB with an extremely unusual bright X-ray plateau and extremely steep decay phase. However, the prompt and late time properties are consistent with typical SGRBs. The plateau is explained by an unstable magnetar, formed during the SGRB, which collapses to form a BH within a few hundred seconds. The magnetar is suggested to be formed via the merger of two NSs. Many Swift SGRBs are shown to have evidence of energy injection within their X-ray lightcurves and 44–76% are consistent with forming a magnetar.