Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Afterglow Lightcurves from Misaligned Structured Jets   GRB 170817A/GW 170817 is the first 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 modeled 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
$\theta_{\rm c}$) and power-law wings in energy per unit solid angle
($\epsilon=\epsilon_c\Theta^{-a}$ where $\Theta=[1+(\theta/\theta_{\rm
c})^2]^{1/2}$) and initial specific kinetic energy ($\Gamma_0-1=[\Gamma_{\rm
c,0}-1]\Theta^{-b}$), as well as briefly discuss Gaussian jets. Our study
reveals qualitatively different types of lightcurves 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 lightcurve shape rather than
the absolute normalizations of times and / or fluxes, removes the dependence of
the lightcurve 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 $\Gamma_{\rm c,0}$ and $b$,
leading to a narrow strip of allowed solutions in the $\Gamma_{\rm c,0}$-$b$
plane above some minimal values $\Gamma_{\rm c,0}\gtrsim 40, b\gtrsim1.2$.
Furthermore, the Lorentz factor of the material dominating the early lightcurve
can be constrained by three independent techniques to be
$\Gamma_{0}(\theta_{\rm min,0})\approx5-7$.

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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: cs
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The categories of this paper are: eess
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The categories of this paper are: q-alg
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: supr-con