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GRB jet structure and the jet break

Lamb, GP, Alexander Kann, D, Fernandez, JJ, Mandel, I, Levan, AJ and Tanvir, NR (2021) GRB jet structure and the jet break. Monthly Notices of the Royal Astronomical Society, 506 (3). pp. 4163-4174. ISSN 0035-8711

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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.

Item Type: Article
Uncontrolled Keywords: AFTERGLOW LIGHT CURVES; Astronomy & Astrophysics; GAMMA-RAY BURST; gamma-ray burst: general; HOST GALAXY; OPTICAL AFTERGLOW; Physical Sciences; PRE-SWIFT; REFRESHED SHOCK; REVERSE SHOCK; Science & Technology; STELLAR WIND; SWIFT OBSERVATIONS; TO-ISM TRANSITION; Science & Technology; Physical Sciences; Astronomy & Astrophysics; gamma-ray burst: general; GAMMA-RAY BURST; AFTERGLOW LIGHT CURVES; TO-ISM TRANSITION; OPTICAL AFTERGLOW; SWIFT OBSERVATIONS; REFRESHED SHOCK; REVERSE SHOCK; STELLAR WIND; HOST GALAXY; PRE-SWIFT; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
SWORD Depositor: A Symplectic
Date Deposited: 26 Jun 2023 12:53
Last Modified: 26 Jun 2023 13:00
DOI or ID number: 10.1093/mnras/stab2071
URI: https://researchonline.ljmu.ac.uk/id/eprint/20076
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