Gamma-Ray Burst Afterglows as probes of their host galaxies and the Cosmos

Open Access
Author:
Cucchiara, Antonino
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 04, 2010
Committee Members:
  • Derek Brindley Fox, Dissertation Advisor
  • Derek Brindley Fox, Committee Chair
  • Michael Eracleous, Committee Member
  • Jane Camilla Charlton, Committee Member
  • Peter Istvan Meszaros, Committee Member
  • Irina Mocioiu, Committee Member
Keywords:
  • Gamma-ray Bursts
  • Afterglow
  • MgII
  • GRB
  • absorbers
  • redshift
Abstract:
Gamma-ray Bursts (GRBs) represent the sole class of catastrophic phenomena seen over almost the entire history of the Universe. Their extreme luminosities in high energy γ-ray radiation make them readily detectable, even with relatively small satellite- based detectors, out to the earliest cosmic epochs. Moreover, the brilliance of their fading afterglow light, routinely observed in X-ray, optical, near-infrared, and radio wavelengths, allows them to be exploited – for hours, days, or weeks – as cosmic lighthouses, probing the conditions of gas and dust along the line of sight, through their host galaxies and the cosmos at large. Since the November 2004 launch of Swift, this GRB-focused NASA mission has discovered more than 500 GRBs, in almost all cases reporting the burst coordinates to ground-based observers within seconds of the event. The availability of prompt burst positions from Swift, combined with promptly-reported flux measurements from instru- ments on Swift and an array of ground-based robotic telescopes, have enabled targeted spectroscopic campaigns that have gathered detailed observations of the young, bright afterglows of hundreds of these events. This thesis reports the results of my own ef- forts over the past 5 years, analyzing imaging and spectroscopic observations of Swift- detected GRBs as triggered according to my own requests, or as gathered from public data archives. In Chapter 2, I discuss our follow-up campaign for GRB 090429B, one of our best “extreme redshift” (z > 8) candidates. This burst followed closely on the spectroscopically- confirmed z = 8.2 GRB 090423, and our multiwavelength observations and SED model- ing demonstrate the value and limitation of such studies, in cases where a spectroscopic redshift cannot be gathered in a timely fashion. I also address the importance of such extreme-redshift events from a cosmological perspective. In Chapter 3, I use high-resolution GRB afterglow spectra to study the properties of intervening absorbers along GRB lines of sight, in particular, the “very strong” Mg ii absorbers, which are often associated with Damped Lyman-α systems. By comparing the properties of the absorbers detected along GRB and quasar lines-of-sight, we attempt to shed light on the mysterious excess of such absorbers in GRB (as compared to quasar) spectra. Carrying out a battery of kinematic and qualitative tests, we fail to identify any respect in which the GRB systems systematically differ from the quasar systems, thus disfavoring the hypothesis that some or many of the GRB absorbers are associated with fast-moving gas in the GRB environs or host galaxy.