Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An annular gap acceleration model for $\gamma$-ray emission of pulsars   If the binding energy of the pulsar's surface is not so high (the case of a
neutron star), both the negative and positive charges will flow out freely from
the surface of the star. The annular free flow model for $\gamma$-ray emission
of pulsars is suggested in this paper. It is emphasized that: (1). Two kinds of
acceleration regions (annular and core) need to be taken into account. The
annular acceleration region is defined by the magnetic field lines that cross
the null charge surface within the light cylinder. (2). If the potential drop
in the annular region of a pulsar is high enough (normally the cases of young
pulsars), charges in both the annular and the core regions could be accelerated
and produce primary gamma-rays. Secondary pairs are generated in both regions
and stream outwards to power the broadband radiations. (3). The potential drop
in the annular region grows more rapidly than that in the core region. The
annular acceleration process is a key point to produce wide emission beams as
observed. (4). The advantages of both the polar cap and outer gap models are
retained in this model. The geometric properties of the $\gamma$-ray emission
from the annular flow is analogous to that presented in a previous work by Qiao
et al., which match the observations well. (5). Since charges with different
signs leave the pulsar through the annular and the core regions, respectively,
the current closure problem can be partially solved.

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The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: econ
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The categories of this paper are: q-fin