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Toward an understanding of the progenitors of gamma-ray bursts

Bloom, Joshua Simon (2002) Toward an understanding of the progenitors of gamma-ray bursts. Dissertation (Ph.D.), California Institute of Technology.


The various possibilities for the origin (``progenitors') of gamma-ray bursts (GRBs) manifest in differing observable properties. Through deep spectroscopic and high-resolution imaging observations of some GRB hosts, I demonstrate that well-localized long-duration GRBs are connected with otherwise normal star-forming galaxies at moderate redshifts of order unity. Using high-mass binary stellar population synthesis models, I quantify the expected spatial extent around galaxies of coalescing neutron stars, one of the leading contenders for GRB progenitors. I then test this scenario by examining the offset distribution of GRBs about their apparent hosts making extensive use of ground-based optical data from Keck and Palomar and space-based imaging from the Hubble Space Telescope. The offset distribution appears to be inconsistent with the coalescing neutron star binary hypothesis (and, similarly, black-hole-neutron star coalescences); instead, the distribution is statistically consistent with a population of progenitors that closely traces the ultra-violet light of galaxies. This is naturally explained by bursts which originate from the collapse of massive stars (``collapsars'). This claim is further supported by the unambiguous detections of intermediate-time (approximately three weeks after the bursts) emission 'bumps' which appear substantially more red than the afterglows themselves. I claim that these bumps could originate from supernovae that occur at approximately the same time as the associated GRB; if true, GRB 980326 and GRB 011121 provide strong observational evidence connecting cosmological GRBs to high-redshift supernovae and implicate massive stars as the progenitors of at least some long-duration GRBs. Regardless of the true physical origin of these bumps, it appears that all viable alternative models of these bumps (such as dust scattering of the afterglow light) require a substantial amount of circumburst matter that is distributed as a wind-stratified medium; this too, implicates massive stars. Also suggested herein are some future observations which could further solidify or refute the supernova claim. In addition to the observational and modeling work, I also constructed the Jacobs Camera (JCAM), a dual-beam optical camera for the Palomar 200-inch Telescope designed to follow-up rapid GRB localizations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:black hole; cosmology; gravitational waves; neutrinos; neutron stars; novae; population III; stars; Type Ic supernova
Degree Grantor:California Institute of Technology
Major Option:Astronomy
Thesis Committee:
  • Harrison, Fiona (chair)
  • Djorgovski, George
  • Kamionkowski, Marc
  • Scoville, Nick
  • Kulkarni, Shri
Defense Date:1 April 2002
Author Email:jbloom (AT)
Record Number:etd-01062003-061357
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38
Deposited By: Imported from ETD-db
Deposited On:06 Jan 2003
Last Modified:25 Dec 2012 14:57

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