Journal Article

Is gamma-ray burst afterglow emission intrinsically anisotropic?

A. M. Beloborodov, F. Daigne, R. Mochkovitch and Z. L. Uhm

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 4, pages 2422-2427
Published in print February 2011 | ISSN: 0035-8711
Published online January 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17616.x
Is gamma-ray burst afterglow emission intrinsically anisotropic?

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The curvature of a relativistic blast wave implies that its emission arrives to observers with a spread in time. This effect is believed to wash out fast variability in the light curves of gamma-ray burst (GRB) afterglows. We note that the spreading effect is reduced if emission is anisotropic in the rest frame of the blast wave (i.e. if emission is limb-brightened or limb-darkened). In particular, synchrotron emission is almost certainly anisotropic, and may be strongly anisotropic, depending on details of electron acceleration in the blast wave. Anisotropic afterglows can display fast and strong variability at high frequencies (above the ‘fast-cooling’ frequency). This may explain the existence of bizarre features in the X-ray afterglows of GRBs, such as sudden drops and flares. We also note that a moderate anisotropy can significantly delay the ‘jet break’ in the light curve, which makes it harder to detect.

Keywords: radiation mechanisms: non-thermal; shock waves; gamma-ray burst: general

Journal Article.  4068 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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