Gamma-ray bursts and their environments

Gamma-ray Bursts (GRBs) are the most energetic explosive events known in the universe and manifest themselves as a brief flash of high energy (X-ray and gamma-ray) photons lasting for a few seconds. Subsequent to the prompt gamma-ray flash, longer lasting afterglow emission is seen at X-ray, optical and radio wavelengths. These afterglows have allowed the precise positioning of GRBs on the sky, redshift measurements and the identification of host galaxies. They have also demonstrated that GRBs with durations of > 2s are relativistically beamed jetted outflows associated with the collapse of massive stars in a type Ic supernova.;In this thesis I present observations of several GRB afterglows and a large survey of GRB host galaxies. The goal of the research is to better understand the connection between GRBs, stellar collapse and star formation. The work presented here demonstrates that GRBs are a diverse population, showing that the supernovae associated with GRBs can span an order of magnitude in absolute luminosity, and are sometimes invisible, even in deep searches.;This work has also located the first good example of a GRB which is heavily optically extinguished due to the presence of dust in its host galaxy, demonstrating that dust extinction can account for a fraction of the "dark bursts", which are invisible at optical wavelengths.;Finally, the connection of GRBs to star formation at large is addressed via a comparison of the properties of the host galaxies of GRBs and core collapse supernovae. I show that GRBs are much more concentrated on their host galaxy light than supernovae and, furthermore, have host galaxies significantly smaller and less luminous that those of SN. Jointly these results indicate that GRBs may originate in low metallicity environments, and come from the most massive stars. This result may have important consequence for the use of GRBs as probes of high redshift star formation.