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Cosmic explosions: the beasts and their lair

Citation

Berger, Edo (2004) Cosmic explosions: the beasts and their lair. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-05202004-165422

Abstract

The diversity of stellar death is revealed in the energy, velocity and geometry of the explosion debris ("ejecta"). Using multi-wavelength observations of gamma-ray burst (GRB) afterglows I show that GRBs, arising from the death of massive stars, are marked by relativistic, collimated ejecta ("jets") with a wide range of opening angles. I further show that the jet opening angles are strongly correlated with the isotropic-equivalent kinetic energies, such that the true relativistic energy of GRBs is nearly standard, with a value of few times 10^51 erg. A geometry-independent analysis which relies on the simple non-relativistic dynamics of GRBs at late time confirms these inferences. Still, the energy in the highest velocity ejecta, which give rise to the prompt gamma-ray emission, is highly variable. These results suggest that various cosmic explosions are powered by a common energy source, an "engine" (possibly an accreting stellar-mass black hole), with their diverse appearances determined solely by the variable high velocity output. On the other hand, using radio observations I show that local type Ibc core-collapse supernovae generally lack relativistic ejecta and are therefore not powered by engines. Instead, the highest velocity debris in these sources, typically with a velocity lower than 100,000 km/sec, are produced in the (effectively) spherical ejection of the stellar envelope. The relative rates of engine- and collapse-powered explosions suggest that the former account for only a small fraction of the stellar death rate. Motivated by the connection of GRBs to massive stars, and by their ability to overcome the biases inhenert in current galaxy surveys, I investigate the relation between GRB hosts and the underlying population of star-forming galaxies. Using the first radio and submillimeter observations of GRB hosts, I show that some are extreme starburst galaxies with the bursts directly associated with the regions of most intense star formation. I suggest, by comparison to other well-studied samples, that GRBs preferentially occur in sub-luminous, low mass galaxies, undergoing the early stages of a starburst process. If confirmed with future observations, this trend will place GRBs in the forefront of star formation and galaxy evolution studies.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Astrophysics; Gamma-ray bursts; High-redshift galaxies; Radio astronomy; Supernovae
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Kulkarni, Shrinivas R.
Thesis Committee:
  • Harrison, Fiona A. (chair)
  • Frail, Dale A.
  • Phinney, E. Sterl
  • Kulkarni, Shrinivas R.
  • Golwala, Sunil
Defense Date:18 May 2004
Author Email:ejb (AT) astro.caltech.edu
Record Number:CaltechETD:etd-05202004-165422
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-05202004-165422
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1892
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:21 May 2004
Last Modified:26 Dec 2012 02:43

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