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GRB jet structure and the jet break

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journal contribution
posted on 2021-08-26, 08:29 authored by Gavin P Lamb, D Alexander Kann, Joseph John Fernández, Ilya Mandel, Andrew J Levan, Nial R Tanvir
We investigate the shape of the jet break in within-beam gamma-ray burst (GRB) optical afterglows for various lateral jet structure profiles. We consider cases with and without lateral spreading and a range of inclinations within the jet core half-opening angle, θc. We fit model and observed afterglow light curves with a smoothly-broken power-law function with a free-parameter κ that describes the sharpness of the break. We find that the jet break is sharper (κ is greater) when lateral spreading is included than in the absence of lateral spreading. For profiles with a sharp-edged core, the sharpness parameter has a broad range of 0.1 ≲ κ ≲ 4.6, whereas profiles with a smooth-edged core have a narrower range of 0.1 ≲ κ ≲ 2.2 when models both with and without lateral spreading are included. For sharp-edged jets, the jet break sharpness depends strongly on the inclination of the system within θc, whereas for smooth-edged jets, κ is more strongly dependent on the size of θc. Using a sample of 20 GRBs, we find 9 candidate smooth-edged jet structures and 8 candidate sharp-edged jet structures, while the remaining 3 are consistent with either. The shape of the jet break, as measured by the sharpness parameter κ, can be used as an initial check for the presence of lateral structure in within-beam GRBs where the afterglow is well-sampled at and around the jet-break time.

History

Citation

Monthly Notices of the Royal Astronomical Society, Volume 506, Issue 3, September 2021, Pages 4163–4174, https://doi.org/10.1093/mnras/stab2071

Author affiliation

School of Physics and Astronomy

Version

  • AM (Accepted Manuscript)

Published in

Monthly Notices of the Royal Astronomical Society

Volume

506

Issue

3

Pagination

4163 - 4174

Publisher

Oxford University Press (OUP)

issn

0035-8711

eissn

1365-2966

Acceptance date

2021-07-15

Copyright date

2021

Available date

2021-08-26

Language

en

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