Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fermi Large Area Telescope Observations of the Active Galaxy 4C +55.17:
  Steady, Hard Gamma-Ray Emission and its Implications   We report Fermi/LAT observations and broad-band spectral modeling of the
radio-loud active galaxy 4C +55.17 (z=0.896), formally classified as a
flat-spectrum radio quasar. Using 19 months of all-sky survey Fermi/LAT data,
we detect a gamma-ray continuum extending up to an observed energy of 145 GeV,
and furthermore we find no evidence of gamma-ray variability in the source over
its observed history. We illustrate the implications of these results in two
different domains. First, we investigate the origin of the steady gamma-ray
emission, where we re-examine the common classification of 4C +55.17 as a
quasar-hosted blazar and consider instead its possible nature as a young radio
source. We analyze and compare constraints on the source physical parameters in
both blazar and young radio source scenarios by means of a detailed
multiwavelength analysis and theoretical modeling of its broad-band spectrum.
Secondly, we show that the gamma-ray spectrum may be formally extrapolated into
the very-high energy (VHE; >= 100 GeV) range at a flux level detectable by the
current generation of ground-based Cherenkov telescopes. This enables us to
place constraints on models of extragalactic background light (EBL) within LAT
energies and features the source as a promising candidate for VHE studies of
the Universe at an unprecedented redshift of z=0.896.

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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
9
The categories of this paper are: nlin
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
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The categories of this paper are: plasm-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: math-ph
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The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci