Nakar, Ehud 2005 SGR 的giant flare的火球模型

主要内容:
内包含初始罗仑兹因子的推导. 重子loading的推导如下:


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Title:		Pure and Loaded Fireballs in Soft Gamma-Ray Repeater Giant Flares
Authors:		Nakar, Ehud; Piran, Tsvi; Sari, Re'em
Affiliation:		AA(Theoretical Astrophysics, California Institute of Technology, MS 130-33, Pasadena, CA 91125.), AB(Theoretical Astrophysics, California Institute of Technology, MS 130-33, Pasadena, CA 91125.; Racah Institute for Physics, Hebrew University, Jerusalem 91904, Israel.), AC(Theoretical Astrophysics, California Institute of Technology, MS 130-33, Pasadena, CA 91125.)
Publication:		The Astrophysical Journal, Volume 635, Issue 1, pp. 516-521. (ApJ Homepage)
Publication Date:		12/2005
Origin:		UCP
ApJ Keywords:		Gamma Rays: Theory, Stars: Individual: Alphanumeric: SGR 1806-20
Abstract Copyright:		(c) 2005: The American Astronomical Society
DOI:		10.1086/497296
Bibliographic Code:		2005ApJ...635..516N

Abstract

On 2004 December 27, a giant flare from SGR 1806-20 was detected on Earth. Its thermal spectrum and temperature suggest that the flare resulted from an energy release of about 10⁴⁷ ergs s^-1 close to the surface of a neutron star in the form of radiation and/or pairs. This plasma expanded under its own pressure, producing a fireball, and the observed gamma rays escaped once the fireball became optically thin. The giant flare was followed by a bright radio afterglow, with an observable extended size, implying an energetic relativistic outflow. We revisit here the evolution of relativistic fireballs, and we calculate the Lorentz factor and energy remaining in relativistic outflow once the radiation escapes. We show that pairs that arise naturally in a pure pair-radiation fireball do not carry enough energy to account for the observed afterglow. We consider various alternatives and show that if the relativistic outflow that causes the afterglow is related directly to the prompt flare, then the initial fireball must be loaded by baryons or Poynting flux. While we focus on parameters applicable to the giant flare and the radio afterglow of SGR 1806-20, the calculations presented here could be also applicable to gamma-ray bursts (GRBs).

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