Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Impulsive and Long Duration High-Energy Gamma-ray Emission From the Very
  Bright 2012 March 7 Solar Flares   The Fermi Large Area Telescope (LAT) observed two bright X-class solar flares
on 2012 March 7, and detected gamma-rays up to 4 GeV. We detected gamma-rays
both during the impulsive and temporally-extended emission phases, with
emission above 100 MeV lasting for approximately 20 hours. Accurate
localization of the gamma-ray production site(s) coincide with the solar active
region from which X-ray emissions associated with these flares originated. Our
analysis of the >100 MeV gamma-ray emission shows a relatively rapid monotonic
decrease in flux during the first hour of the impulsive phase, and a much
slower, almost monotonic decrease in flux for the next 20 hours. The spectra
can be adequately described by a power law with a high energy exponential
cutoff, or as resulting from the decay of neutral pions produced by accelerated
protons and ions with an isotropic power-law energy distribution. The required
proton spectrum has a number index ~3, with minor variations during the
impulsive phase, while during the temporally extended phase the spectrum
softens monotonically, starting with index ~4. The >30 MeV proton flux and
spectra observed near the Earth by the GOES satellites also show a monotonic
flux decrease and spectral softening during the extended phase, but with a
harder spectrum, with index ~3. Based on the Fermi-LAT and GOES observations of
the flux and spectral evolution of these bright flares, we explore the relative
merits of prompt and continuous acceleration scenarios, hadronic and leptonic
emission processes, and acceleration at the solar corona by the fast Coronal
Mass Ejections (CME) as explanations for the observations. We conclude that the
most likely scenario is continuous acceleration of protons in the solar corona
which penetrate the lower solar atmosphere and produce pions that decay into
gamma-rays.

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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: stat
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The categories of this paper are: supr-con
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: q-alg
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The categories of this paper are: chem-ph
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The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
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The categories of this paper are: cond-mat