Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010phdt.......197c&link_type=abstract
ProQuest Dissertations And Theses; Thesis (Ph.D.)--The Pennsylvania State University, 2010.; Publication Number: AAT 3436130; IS
Mathematics
Logic
Scientific paper
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 gamma-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 instruments 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 efforts 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 GRB090429B, one of our best "extreme redshift" (z > 8) candidates. This burst followed closely on the spectroscopicallyconfirmed z = 8.2 GRB090423, and our multiwavelength observations and SED modeling 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-alpha 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. In Chapter 4, I present a summary of five years of GRB afterglow spectroscopic follow-up efforts, the Gemini catalog of mid-resolution afterglow spectra. This dataset consists of more than 50 GRBs observed with the GMOS instruments on the Gemini North and South telescopes; among these objects, we select 22 high signal-to-noise spectra for comprehensive analysis, reporting equivalent widths and upper or lower limits for a large number of atomic species often observed in absorption in GRB afterglow spectra. Applying these results, we explore the metallicity and dust content of the host galaxies of these GRBs, since these properties likely have important implications for the nature of the progenitors and the characterization of the GRB environment. Finally, in my conclusions, I review what we have learned over the past five years, and address some of the open questions in the use of GRB afterglows as cosmic probes that I expect will attract the greatest attention of researchers over the next few years.
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