Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of VHE Gamma-ray Emission from the Starburst Galaxy M82   The galaxy M82 has long been considered a promising target for VHE gamma-ray
observations because of the compact starburst region in its core. Theoretical
predictions have suggested it should be detectable by ground-based imaging
Cherenkov telescopes like VERITAS and that a detection would have implications
for the understanding of the origin of cosmic rays. M82 was observed with the
VERITAS array during the 2007-2009 observing seasons. With an exposure of 137
hours, VERITAS was able to detect a gamma-ray signal at the 5 sigma level. This
marks the discovery of gamma rays not only from M82 but also from the new
source class of starburst galaxies. The observed flux from M82 is 3.7\pm
0.8(stat)\pm 0.7(syst)x10^-13 photons cm^-2 s^-1 above an energy threshold of
700 GeV, which corresponds to 0.9% of the Crab Nebula flux. The differential
energy spectrum is a power law with a photon index Gamma=2.5\pm 0.6(stat)\pm
0.2(syst). Both the flux and the photon index is close to recent theoretical
predictions. The VERITAS data places a strong correlation between the
star-formation activity and the cosmic-ray production in M82.

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The categories of this paper are: adap-org
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: alg-geom
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
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The categories of this paper are: cond-mat
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The categories of this paper are: mtrl-th