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 SNR G54.1+0.3   We report the discovery of very high energy gamma-ray emission from the
direction of the SNR G54.1+0.3 using the VERITAS ground-based gamma-ray
observatory. The TeV signal has an overall significance of 6.8$\sigma$ and
appears point-like given the 5$^{arcminute}$ resolution of the instrument. The
integral flux above 1 TeV is 2.5% of the Crab Nebula flux and significant
emission is measured between 250 GeV and 4 TeV, well described by a power-law
energy spectrum dN/dE $\sim$ E$^{-\Gamma}$ with a photon index $\Gamma=
2.39\pm0.23_{stat}\pm0.30_{sys}$. We find no evidence of time variability among
observations spanning almost two years. Based on the location, the morphology,
the measured spectrum, the lack of variability and a comparison with similar
systems previously detected in the TeV band, the most likely counterpart of
this new VHE gamma-ray source is the PWN in the SNR G54.1+0.3. The measured
X-ray to VHE gamma-ray luminosity ratio is the lowest among all the nebulae
supposedly driven by young rotation-powered pulsars, which could indicate a
particle-dominated PWN.

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The categories of this paper are: alg-geom
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The categories of this paper are: physics
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The categories of this paper are: stat
2
The categories of this paper are: math
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The categories of this paper are: cs
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: eess
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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: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: ao-sci