TY - JOUR

T1 - Afterglow light curves from misaligned structured jets

AU - Beniamini, Paz

AU - Granot, Jonathan

AU - Gill, Ramandeep

N1 - Publisher Copyright:
© 2020 The Author(s).

PY - 2020/4/1

Y1 - 2020/4/1

N2 - GRB170817A/GW 170817 is the first gamma-ray burst (GRB) clearly viewed far from the GRBjet's symmetry axis. Its afterglowwas denselymonitored 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 θc) and power-law wings in energy per unit solid angle (ϵ= ϵcΘ-a where Θ = [1 + (θ/θc)2]1/2) and initial specific kinetic energy (γ0 - 1 = [γc, 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 γc, 0 and b, leading to a narrow strip of allowed solutions in the γc, 0-b plane above some minimal values γc, 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(θmin, 0) ≈ 5-7.

AB - GRB170817A/GW 170817 is the first gamma-ray burst (GRB) clearly viewed far from the GRBjet's symmetry axis. Its afterglowwas denselymonitored 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 θc) and power-law wings in energy per unit solid angle (ϵ= ϵcΘ-a where Θ = [1 + (θ/θc)2]1/2) and initial specific kinetic energy (γ0 - 1 = [γc, 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 γc, 0 and b, leading to a narrow strip of allowed solutions in the γc, 0-b plane above some minimal values γc, 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(θmin, 0) ≈ 5-7.

KW - Gamma-ray burst: general

KW - Radiation mechanisms: general

UR - http://www.scopus.com/inward/record.url?scp=85085370655&partnerID=8YFLogxK

U2 - 10.1093/mnras/staa538

DO - 10.1093/mnras/staa538

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AN - SCOPUS:85085370655

SN - 0035-8711

VL - 493

SP - 3521

EP - 3534

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 3

ER -