Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multi-wavelength observations of PKS 2155-304 with H.E.S.S   The High Energy Stereoscopic System (H.E.S.S.) has observed the
high-frequency peaked BL Lac object PKS2155-304 in 2003 between October 19 and
November 26 in Very High Energy (VHE) gamma-rays (E>160 GeV for these
observations). Observations were carried out simultaneously with the
Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer
satellite (RXTE), the Robotic Optical Transient Search Experiment (ROTSE) and
the Nancay decimetric radiotelescope (NRT). Intra-night variability is seen in
the VHE band, the source being detected with a high significance on each night
it was observed. Variability is also found in the X-ray and optical bands on
kilosecond timescales, along with flux-dependent spectral changes in the
X-rays. The average H.E.S.S. spectrum shows a very soft power law shape with a
photon index of 3.37+/-0.07(stat)+/-0.10(sys). The energy outputs in the 2-10
keV and in the VHE gamma-ray range are found to be similar, with the X-rays and
the optical fluxes at a level comparable to some of the lowest historical
measurements, indicating that PKS2155-304 was in a low or quiescent state
during the observations. Both a leptonic and a hadronic model are used to
derive source parameters from these observations.

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The categories of this paper are: solv-int
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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: q-alg
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The categories of this paper are: hep-ph
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The categories of this paper are: physics
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: stat
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The categories of this paper are: cond-mat