Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-Resolution Spectroscopy of Gamma-Ray Lines from the X-Class Solar
  Flare of 23 July, 2002   The Reuven Ramaty High Energy Solar Spectroscopy Imager (RHESSI) has obtained
the first high-resolution measurements of nuclear de-excitation lines produced
by energetic ions accelerated in a solar flare, a GOES X4.8 event occurring on
23 July, 2002 at a heliocentric angle of 73 degrees. Lines of neon, magnesium,
silicon, iron, carbon, and oxygen were resolved for the first time. They
exhibit Doppler redshifts of 0.1--0.8% and broadening of 0.1--2.1% (FWHM),
generally decreasing with mass. The measured redshifts are larger than expected
for a model of an interacting ion distribution isotropic in the downward
hemisphere in a radial magnetic field. Possible interpretations of the large
redshifts include 1) an inclination of the loop magnetic field to the solar
surface so that the ion distribution is oriented more directly away from the
observer, and 2) extreme beaming of the ions downward along a magnetic field
normal to the solar surface. Bulk downward motion of the plasma in which the
accelerated ions interact can be ruled out.

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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: hep-lat
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The categories of this paper are: nucl-th
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The categories of this paper are: cs
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: eess
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: cond-mat