PhD Defense Konstantinos Leventis
Gamma-ray bursts (GRBs) are the most powerful sources of electromagnetic radiation in the universe. They are the result of a catastrophic event, like the collapse of a very massive star or the collision of two compact objects (e.g. neutron stars). The gamma rays we observe originate from shocks within the relativistic outflow that is ejected from the burster. However, as the outflow interacts with the surrounding medium it gives rise to the afterglow radiation, which typically lasts longer and is observed over a broader range of frequencies, compared to the bursts itself.
Modelling the afterglow emission is one of the most powerful methods of probing the nature and physical processes of GRBs and their progenitors. In this Thesis, I explore various phases of the afterglow dynamics and the resulting spectra and light curves. I show that the transition of the outflow to non-relativistic velocities is manifested slowly in the observer's frame and quantify the properties of the transition across the spectrum. This has resulted in a set of flux prescriptions that I have used to accurately infer physical parameters of individual bursts. Beyond late-time behaviour, I have also looked into the early afterglow, for which I have analysed the observational signatures of energy injection into the blast wave, over a prolonged period. This analysis strongly suggests that the reverse shock significantly contributes to, and in some cases even dominates, the emission during the plateau phase of GRB afterglows.
Location: Agnietenkapel, Oudezijds Voorburgwal 231, Amsterdam