Journal Article

Jet simulations and gamma-ray burst afterglow jet breaks

H. J. van Eerten, Z. Meliani, R. A. M. J. Wijers and R. Keppens

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 3, pages 2016-2024
Published in print January 2011 | ISSN: 0035-8711
Published online January 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17582.x
Jet simulations and gamma-ray burst afterglow jet breaks

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The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on circumstances, the radio jet break may be postponed significantly. Using high-accuracy adaptive mesh fluid simulations in one dimension, coupled to a detailed synchrotron radiation code, we demonstrate that this is true even for the standard fireball model and hard-edged jets. We confirm these effects with a simulation in two dimensions. The frequency dependence of the jet break is a result of the angle dependence of the emission, the changing optical depth in the self-absorbed regime and the shape of the synchrotron spectrum in general. In the optically thin case the conventional analysis systematically overestimates the jet break time, leading to inferred opening angles that are underestimated by a factor of ∼1.3 and explosion energies that are underestimated by a factor of ∼1.7, for explosions in a homogeneous environment. The methods presented in this paper can be applied to adaptive mesh simulations of arbitrary relativistic fluid flows. All analysis presented here makes the usual assumption of an on-axis observer.

Keywords: hydrodynamics; radiation mechanisms: non-thermal; shock waves; gamma-ray burst: general; gamma-ray burst: individual: GRB030329; X-rays: general

Journal Article.  7443 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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