Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observations of Gamma-ray emission from the blazar Markarian 421 above
  250 GeV with the CAT Cherenkov imaging telescope   The gamma-ray emission of the blazar Markarian 421 above 250 GeV has been
observed by the CAT Cherenkov imaging telescope since December, 1996. We report
here results on the source variability up to April, 1998, with emphasis on the
1998 campaign. For the flaring periods of this year, the energy spectrum was
derived from 330 GeV up to 5.2 TeV: it is very well represented by a simple
power law, with a differential spectral index of 2.96 +/- 0.13.

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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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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: hep-lat
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The categories of this paper are: supr-con
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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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: plasm-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: math
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: cs