Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Probing the Puzzle of Behind-the-Limb $\gamma$-ray Flares: Data-driven
  Simulations of Magnetic Connectivity and CME-driven Shock Evolution   Recent detections of high-energy $\gamma$-rays from behind-the-limb (BTL)
solar flares by the \emph{Fermi $\gamma$-ray Space Telescope} pose a puzzle and
challenge on the particle acceleration and transport mechanisms. In such
events, the $\gamma$-ray emission region is located away from the BTL flare
site by up to tens of degrees in heliogrpahic longitude. It is thus
hypothesized that particles are accelerated at the shock driven by the coronal
mass ejection (CME) and then travel from the shock downstream back to the front
side of the Sun to produce the observed $\gamma$-rays. To test this scenario,
we performed data-driven, global magnetohydrodynamics simulations of the CME
associated with a well-observed BTL flare on 2014 September 1. We found that
part of the CME-driven shock develops magnetic connectivity with the
$\gamma$-ray emission region, facilitating transport of particles back to the
Sun. Moreover, the observed increase in $\gamma$-ray flux is temporally
correlated with (1) the increase of the shock compression ratio and (2) the
presence of a quasi-perpendicular shock over the area that is magnetically
connected to the $\gamma$-ray emitting region, both conditions favoring the
diffusive shock acceleration (DSA) of particles. These results support the
above hypothesis and can help resolve another puzzle, i.e., long-duration (up
to 20 hours) $\gamma$-rays flares. We suggest that, in addition to DSA,
stochastic acceleration by plasma turbulence may also play a role, especially
in the shock downstream region and during the early stage when the shock
Alfv\'{e}n Mach number is small.

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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: physics
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol
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The categories of this paper are: econ
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: eess