X-ray, Ultraviolet, and Optical Flares in Gamma-ray Burst Light Curves

Open Access
Author:
Swenson, Craig Arnel
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 13, 2014
Committee Members:
  • Pete Roming, Dissertation Advisor
  • John Andrew Nousek, Committee Chair
  • Eric D Feigelson, Committee Member
  • Derek Brindley Fox, Committee Member
  • Stephane Coutu, Special Member
Keywords:
  • astronomy
  • astrophysics
  • GRB
  • gamma-ray burst
  • Swift
  • bayesian
Abstract:
One of the surprising results of the NASA Swift mission was the discovery of large numbers of flares in gamma-ray burst (GRB) light curves. Though they had previously been seen, the Swift data showed that flares appear in approximately 50% of X-ray GRB light curves. Many of these flares are very large and energetic, and a number of studies have been performed analyzing the properties of the observed X-ray flares. Flares in the UV and optical wavelengths have not received the same attention due to the flares being smaller and more difficult to identify in the UV/optical. This dissertation presents a new algorithm for detecting flares which we employ on the data from the Second UVOT GRB Catalog, finding 119 flaring periods, most of which are previously unreported. We also present our analysis of the Swift X-ray data from 2005 January through 2012 December, where we find 498 flaring periods, many representing weaker flares that have not been included in previous studies. Our analysis of these two catalogs shows that the our previous understanding and assumptions about flare properties were very limited, particularly in terms of flare duration, with many of our newly identified flares exhibiting durations of ∆t/t > 1. Our correlation studies between the UV/optical and X-ray flares shows that X-ray flares are generally larger, both in terms of duration and flux, than their lower energy counterparts and we discuss possible reasons for this trend. We further discuss whether the emission mechanism causing the observed X-ray and UV/optical flares is the same, and contrast the potentially correlated X-ray and UV/optical flares with flares that have no observed counterpart. The broad range of flare properties observed and the number of UV/optical flares observed without X-ray counterparts lead us to believe that the generally assumed internal shock mechanism may not be correct for all GRB flares and that further theoretical work is needed to explain the observed flare parameters.