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Afterglow light curves from misaligned structured jets

Beniamini, Paz and Granot, Jonathan and Gill, Ramandeep (2020) Afterglow light curves from misaligned structured jets. Monthly Notices of the Royal Astronomical Society, 493 (3). pp. 3521-3534. ISSN 0035-8711. doi:10.1093/mnras/staa538.

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GRB 170817A/GW 170817 is the first gamma-ray burst (GRB) clearly viewed far from the GRB jet’s symmetry axis. Its afterglow was densely monitored over a wide range of frequencies and times. It has been modelled extensively, primarily numerically, and although this endeavour was very fruitful, many of the underlying model parameters remain undetermined. We provide analytic modelling of GRB afterglows observed off-axis, considering jets with a narrow core (of half-opening angle θ_c) and power-law wings in energy per unit solid angle (ϵ = ϵ_cΘ^(−a)) where Θ = [1 + (θ/θ_c)²]^(1/2)) and initial specific kinetic energy (Γ₀ − 1 = [Γ_(c, 0) − 1]Θ^(−b)), as well as briefly discuss Gaussian jets. Our study reveals qualitatively different types of light curves that can be viewed in future off-axis GRBs, with either single or double peaks, depending on the jet structure and the viewing angle. Considering the light-curve shape rather than the absolute normalizations of times and/or fluxes, removes the dependence of the light curve on many of the highly degenerate burst parameters. This study can be easily used to determine the underlying jet structure, significantly reduce the effective parameter space for numerical fitting attempts and provide physical insights. As an illustration, we show that for GRB 170817A, there is a strong correlation between the allowed values of Γ_(c, 0) and b, leading to a narrow strip of allowed solutions in the Γ_(c, 0)–b plane above some minimal values Γ_(c, 0) ≳ 40, b ≳ 1.2. Furthermore, the Lorentz factor of the material dominating the early light curve can be constrained by three independent techniques to be Γ₀ (θ_(min, 0)) ≈ 5–7.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Beniamini, Paz0000-0001-7833-1043
Granot, Jonathan0000-0001-8530-8941
Gill, Ramandeep0000-0003-0516-2968
Alternate Title:Afterglow Lightcurves from Misaligned Structured Jets
Additional Information:© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 February 21. Received 2020 February 21; in original form 2020 January 7; Published: 25 February 2020. PB’s research was funded in part by the Gordon and Betty Moore Foundation through grant GBMF5076. This research was also supported by the Israel Science Foundation (ISF)-National Natural Science Foundation of China (NSFC) joint research program (grant no. 3296/19; RG and JG). PB thanks Wenbin Lu, Geoffrey Ryan, Pawan Kumar, and Ilaria Caiazzo for helpful discussions. We also thank Shiho Kobayashi for useful comments and the anonymous referee for a constructive report.
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5076
Israel Science FoundationUNSPECIFIED
National Natural Science Foundation of China3296/19
Subject Keywords:radiation mechanisms: general – gamma-ray burst: general
Issue or Number:3
Record Number:CaltechAUTHORS:20200430-105723843
Persistent URL:
Official Citation:Paz Beniamini, Jonathan Granot, Ramandeep Gill, Afterglow light curves from misaligned structured jets, Monthly Notices of the Royal Astronomical Society, Volume 493, Issue 3, April 2020, Pages 3521–3534,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102928
Deposited By: Tony Diaz
Deposited On:30 Apr 2020 18:14
Last Modified:16 Nov 2021 18:16

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