Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: GRB 170817A Afterglow from a Relativistic Electron-Positron Pair Wind
  Observed Off-axis   A relativistic electron-positron ($e^{+}e^{-}$) pair wind from a rapidly
rotating, strongly magnetized neutron star (NS) would interact with a gamma-ray
burst (GRB) external shock and reshapes afterglow emission signatures. Assuming
that the merger remnant of GW170817 is a long-lived NS, we show that a
relativistic $e^{+}e^{-}$ pair wind model with a simple top-hat jet viewed
off-axis can reproduce multi-wavelength afterglow lightcurves and superluminal
motion of GRB 170817A. The Markov chain Monte Carlo (MCMC) method is adopted to
obtain the best-fitting parameters, which give the jet half-opening angle
$\theta_{j}\approx0.11$ rad, and the viewing angle $\theta_{v}\approx0.23$ rad.
The best-fitting value of $\theta_{v}$ is close to the lower limit of the prior
which is chosen based on the gravitational-wave and electromagnetic
observations. In addition, we also derive the initial Lorentz factor
$\Gamma_{0}\approx47$ and the isotropic kinetic energy $E_{\rm
K,iso}\approx2\times10^{52}\rm\ erg$. A consistence between the corrected
on-axis values for GRB 170817A and typical values observed for short GRBs
indicates that our model can also reproduce the prompt emission of GRB 170817A.
An NS with a magnetic field strength $B_{p}\approx1.6\times10^{13}\rm\ G$ is
obtained in our fitting, indicating that a relatively low thermalization
efficiency $\eta\lesssim10^{-3}$ is needed to satisfy observational constraints
on the kilonova. Furthermore, our model is able to reproduce a late-time
shallow decay in the X-ray lightcurve and predicts that the X-ray and radio
flux will continue to decline in the coming years.

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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: patt-sol
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The categories of this paper are: nlin