Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the spine-layer scenario for the very high-energy emission of NGC
  1275   We discuss the $\gamma$-ray emission of the radiogalaxy NGC 1275 (the central
galaxy of the Perseus Cluster), detected by Fermi-LAT and MAGIC, in the
framework of the "spine-layer" scenario, in which the jet is assumed to be
characterized by a velocity structure, with a fast spine surrounded by a slower
layer. The existence of such a structure in the parsec scale jet of NGC 1275
has been recently proved through VLBI observations. We discuss the constraints
that the observed spectral energy distribution imposes to the parameters and we
present three alternative models, corresponding to three different choices of
the angles between the jet and the line of sight ($\theta_{\rm v}=6^{\circ},
18^{\circ}$ and 25$^{\circ}$). While for the the case with $\theta_{\rm
v}=6^{\circ}$ we obtain an excellent fit, we consider this solution unlikely,
since such small angles seems to be excluded by radio observations of the
large-scale jet. For $\theta_{\rm v}=25^{\circ}$ the required large intrinsic
luminosity of the soft (IR--optical) component of the spine determines a large
optical depth for $\gamma$-rays through the pair production scattering $\gamma
\gamma\rightarrow e^+ e^-$, implying a narrow cut--off at $\sim50$~GeV. We
conclude that intermediate angles are required. In this case the low frequency
and the high--energy emissions are produced by two separate regions and, in
principle, a full variety of correlations is expected. The correlation observed
between the optical and the $\gamma$-ray flux, close to linearity, is likely
linked to variations of the emissivity of the spine.

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The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
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The categories of this paper are: mtrl-th
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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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: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
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The categories of this paper are: stat
1
The categories of this paper are: cs
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The categories of this paper are: dg-ga