Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: VHE gamma-ray observations of Markarian 501   Markarian 501, a nearby (z=0.033) X-ray selected BL Lacertae object, is a
well established source of Very High Energy (VHE, E>=300 GeV) gamma rays.
Dramatic variability in its gamma-ray emission on time-scales from years to as
short as two hours has been detected. Multiwavelength observations have also
revealed evidence that the VHE gamma-ray and hard X-ray fluxes may be
correlated. Here we present results of observations made with the Whipple
Collaboration's 10 m Atmospheric Cerenkov Imaging Telescope during 1999 and
discuss them in the context of observations made on Markarian 501 during the
period from 1996-1998.

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The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
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The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
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The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph