Gamma-Ray Burst host Galaxies at high resolution

GRBs are the most powerful explosions in the universe and a very interesting phenomenon in themselves. Even though they are the brightest objects detected, they are nevertheless only stellar explosions or mergers of compact objects. Since their discovery in 1967, a lot of progress has been made in identifying them as high redshift events, investigating their high energy and afterglow properties, dividing them into subgroups of long and short duration GRBs with likely different origins and studying their host galaxies. As more and better sampled data become available, notably since the launch of the Swift satellite (Nov. 2004), explanations for what actually happens in the explosion start to be more complicated and more questions are raised than answered.

The following thesis does not deal with the GRB phenomenon itself but it is studying their environment and host galaxies through optical spectroscopy and using them as lightsources in the distant universe. The work is divided in three parts.

The first Chapter gives in introduction to the history of the GRB discovery and research, explains the processes involved in producing a GRB and its afterglow radiation and the different progenitor models for GRBs. It also summarizes the properties of its host galaxies and the differences between short and long GRB hosts. Finally, an overview is given over the fast follow-up observing strategies for GRB afterglows, the special type of proposals needed, and some examples are mentionied in which the author of this thesis was involved in.

Part II presents three examples of using GRBs as powerful lightsources that allow to study the high redshift universe with low and high resolution spectrosocpy. An introduction to the methods of how to observe the high redshift universe is given, what information can be obtained from high resolution spectra and what they tell us about the environment and host galaxy of a GRB. For the first case, GRB 060526, follow-up observations from a large range of telescopes were put together in order to study its afterglow properties. This luminous GRB also allowed us to obtain a dataset of low to medium resolution spectra with FORS 1 at the VLT. A range of UV restframe metal absorption lines are detected of which we determine the column densitiy with the CoG method and subsequently the metallicity.

The next Chapter presents high resolution spectra of the afterglow of GRB 030329 that has both resolved absorption and emission lines, which was possible due to the low redshift of the GRB of z=0.1686. The absorption lines split up in different components with a range of 230 km/s blueshifted compared to the host. We argue that they likely originate from a starburst wind outflow as observed in some nearby starburst galaxies, e.g. M 82.