Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Collisionless Weibel shocks and electron acceleration in gamma-ray
  bursts   A study of collisionless external shocks in gamma-ray bursts is presented.
The shock structure, electromagnetic fields, and process of electron
acceleration are assessed by performing a self-consistent 3D particle-in-cell
(PIC) simulation. In accordance with hydrodynamic shock systems, the shock
consists of a reverse shock (RS) and forward shock (FS) separated by a contact
discontinuity (CD). The development and structure are controlled by the ion
Weibel instability. The ion filaments are sources of strong transverse
electromagnetic fields at both sides of the double shock structure over a
length of 30 - 100 ion skin depths. Electrons are heated up to a maximum energy
$\epsilon_{\rm ele}\approx \sqrt{\epsilon_{\rm b}}$, where $\epsilon$ is the
energy normalized to the total incoming energy. Jet electrons are trapped in
the RS transition region due to the presence of an ambipolar electric field and
reflection by the strong transverse magnetic fields in the shocked region. In a
process similar to shock surfing acceleration (SSA) for ions, electrons
experience drift motion and acceleration by ion filament transverse electric
fields in the plane perpendicular to the shock propagation direction.
Ultimately accelerated jet electrons are convected back into the upstream.

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The categories of this paper are: chem-ph
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The categories of this paper are: funct-an
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The categories of this paper are: cmp-lg
2
The categories of this paper are: math
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The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
5
The categories of this paper are: gr-qc