Gamma-ray bursts : cosmological probes and their connection to supernovae

Abstract

Observed from the nearest galaxies to the beginning of times, Gamma-ray bursts (GRBs) remain the most energetic event in the Universe known to date. As their cone of light travels through the cosmos, the imprint of everything in its path is embedded in the spectra and light curves we observe, providing us with the three dimensional map of matter. This thesis studies the statistical properties of strong MgII absorbers found along the line of sight to GRBs. Firstly, the possibility that the over abundance of these systems could be due to strong gravitational lensing bias is tested. While it is probable that the detection of GRBs and their counterparts in two independent bands ($\gamma$-rays and optical) leads to some lensing bias, it is found that it can not fully resolve the discrepancy in the statistics for these over-common absorbers. After ruling lensing as a potential explanation, a test for the statement that strong MgII are over abundant towards GRBs is conducted, finding that this observation is likely to suffer from low number statistics and can be made insignificant when considering dust obscuration towards the test sample of quasars. Beyond their capability to serve as cosmological probes, GRBs are a fascinating physical phenomenon. Focusing on long GRBs, which are believed to be associated with core-collapse supernovae (CC SNe), the following simulations are developed: evolving a pre- main sequence star using artificial mass loss recipe until before its core collapses --> parameterising the central engine with a piston driven explosion and following the hydrodynamics until the ejecta reaches homologous expansion --> solving for the post-explosion abundances using a post processing nuclear network --> using a radiative transfer (RT) code to calculate the observable properties of the SNe. Since the RT has never been previously used for CC SNe, a comparison of this code to what has been previously used for these SNe is made. The superiority of the code used in this thesis is proven by its ability to not only reproduce the main spectral features found in previous results, but to change the expectation of luminosity from the different viewing angles which could be done due to this coherent time dependent code. An observer located off the GRB axis is actually found to observe a brighter SN than the observe who detected the GRB itself. Once the proficiency of the RT code was proven, a grid of model spanning different explosion parameters and progenitor properties is created. An array of degeneracies between the model parameters is found, proving that using the Arnett relation for estimating the explosion energy and ejected progenitor mass suffers from large uncertainties."