Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of VHE gamma-rays from the BL Lac object PKS 0548-322   PKS 0548-322 (z=0.069) is a ``high-frequency-peaked'' BL Lac object and a
candidate very high energy (VHE, E>100 GeV) gamma-ray emitter, due to its high
X-ray and radio flux. Observations at the VHE band provide insights into the
origin of very energetic particles present in this source and the radiation
processes at work. We report observations made between October 2004 and January
2008 with the H.E.S.S. array, a four imaging atmospheric-Cherenkov telescopes.
Contemporaneous UV and X-ray observations with the Swift satellite in November
2006 are also reported. PKS 0548-322 is detected for the first time in the VHE
band with H.E.S.S. We measure an excess of 216 gamma-rays corresponding to a
significance of 5.6 standard deviations. The photon spectrum of the source is
described by a power-law, with a photon index of Gamma=2.86 +/- 0.34 (stat) +/-
0.10 (sys). The integral flux above 200 GeV is 1.3 % of the flux of the Crab
Nebula, and is consistent with being constant in time. Contemporaneous
Swift/XRT observations reveal an X-ray flux between 2 and 10 keV of F_{2-10
keV}=2.3 +/- 0.2 x 10^{-11} erg.cm^{-2}. s^{-1}, an intermediate intensity
state with respect to previous observations. The spectral energy distribution
can be reproduced using a simple one-zone synchrotron self Compton model, with
parameters similar those observed for other sources of this type.

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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: atom-ph
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The categories of this paper are: stat
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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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: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: cond-mat
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The categories of this paper are: math