Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetar Giant Flares in Multipolar Magnetic Fields --- I. Fully and
  Partially Open Eruptions of Flux Ropes   We propose a catastrophic eruption model for magnetar's enormous energy
release during giant flares, in which a toroidal and helically twisted flux
rope is embedded within a force-free magnetosphere. The flux rope stays in
stable equilibrium states initially and evolves quasi-statically. Upon the loss
of equilibrium point is reached, the flux rope cannot sustain the stable
equilibrium states and erupts catastrophically. During the process, the
magnetic energy stored in the magnetosphere is rapidly released as the result
of destabilization of global magnetic topology. The magnetospheric energy that
could be accumulated is of vital importance for the outbursts of magnetars. We
carefully establish the fully open fields and partially open fields for various
boundary conditions at the magnetar surface and study the relevant energy
thresholds. By investigating the magnetic energy accumulated at the critical
catastrophic point, we find that it is possible to drive fully open eruptions
for dipole dominated background fields. Nevertheless, it is hard to generate
fully open magnetic eruptions for multipolar background fields. Given the
observational importance of the multipolar magnetic fields in the vicinity of
the magnetar surface, it would be worthwhile to explore the possibility of the
alternative eruption approach in multipolar background fields. Fortunately, we
find that flux ropes may give rise to partially open eruptions in the
multipolar fields, which involve only partial opening up of background fields.
The energy release fractions are greater for cases with central-arcaded
multipoles than those with central-caved multipoles emerged in background
fields. Eruptions would fail only when the centrally-caved multipoles become
extremely strong.

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The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: mtrl-th
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The categories of this paper are: econ
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The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: math-ph
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The categories of this paper are: cs
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The categories of this paper are: dg-ga