Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gamma Ray Astronomy with Underground Detectors   Underground detectors measure the directions of up-coming muons of neutrino
origin. They can also observe down-going muons made by gamma rays in the
Earth's atmosphere. Although gamma ray showers are muon-poor, they produce a
sufficient number of muons to detect the sources observed by GeV and TeV
telescopes. With a threshold higher by one hundred and a probability of muon
production of about $1\%$ for the shallower AMANDA and Lake Baikal detectors,
these instruments can, for a typical GRO source, match the detection efficiency
of a GeV satellite detector since their effective area is larger by a factor
$10^4$. The muons must have enough energy for accurate reconstruction of their
direction. Very energetic muons on the other hand are rare because they are
only produced by higher energy gamma rays whose flux is suppressed by the
decreasing flux at the source and by absorption on interstellar light. We show
that there is a window of opportunity for muon astronomy in the 100~GeV energy
region which nicely matches the threshold energies of the AMANDA and Lake
Baikal detectors.

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The categories of this paper are: cond-mat
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The categories of this paper are: math
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The categories of this paper are: comp-gas
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The categories of this paper are: gr-qc
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: physics
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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: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex