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Analytical solutions for expanding fireballs

Li, Chao and Sari, Re'em (2008) Analytical solutions for expanding fireballs. Astrophysical Journal, 677 (1). pp. 425-431. ISSN 0004-637X. doi:10.1086/527551.

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Many models of gamma-ray bursts (GRBs) as well as of soft gamma repeaters (SGRs) involve a fireball — an optically thick concentration of radiation energy with a high ratio of energy density to rest mass. We study the asymptotic behavior of an ultrarelativistic fireball consisting of electron-positron pairs and photons. We show that in the ultrarelativistic limit, after photons decouple from the pairs, the photon distribution function remains a blackbody spectrum in some appropriate Lorentz frame, allowing us to define an effective Lorentz factor and temperature for the photon gas. We also study the freezing out of electron-positron pairs and their asymptotic Lorentz factor γ∞. The dependence of these quantities on initial conditions can be described by simple scaling laws. We apply our results to SGR 1806-20 and find that the energy carried by electron-positron pairs is higher than calculated by former estimates, but is still an order of magnitude short of the minimum energy required to produce the observed afterglow. A viable solution of the energy budget is that the fireball is loaded by baryons or electromagnetic flux.

Item Type:Article
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Sari, Re'em0000-0002-1084-3656
Additional Information:© 2008 The American Astronomical Society. Received 2007 January 16; accepted 2007 December 9. We thank Ehud Nakar and Ben Collins for useful discussion and correcting earlier versions of this manuscript. C. L. is supported by a Betty and Gordon Moore Fellowship. R. S. is a Packard Fellow and an Alfred P. Sloan Fellow. This research was partially supported by a NASA ATP grant.
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Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:gamma rays: bursts; hydrodynamics; radiative transfer
Issue or Number:1
Record Number:CaltechAUTHORS:LICapj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13843
Deposited By: Tony Diaz
Deposited On:06 Apr 2009 21:24
Last Modified:08 Nov 2021 22:41

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