Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Active Galaxies as Particle Accelerators   We present the theoretical arguments and describe the accumulating
experimental evidence that jets, powered by supermassive black holes, are true
cosmic accelerators. They produce photons of TeV energy, possible higher, and
may be the enigmatic source of the highest energy cosmic rays. The features of
the multi-wavelength emission spectrum are dictated by the interactions of
electrons and protons, accelerated in the vicinity of the black hole, with the
ambient light in the galaxy. Photoproduction of neutral pions by protons on UV
light is the source of the highest energy photons, in which most of the
bolometric luminosity of the galaxy may be emitted. They initiate an
electromagnetic cascade which via pair production on the magnetic field and
photon-photon interactions determines the emerging gamma-ray spectrum at lower
energies. The lower energy photons, observed by conventional astronomical
techniques, are, as a result of the cascade process, several generations
removed from the primary high energy beams. The case that proton beams power
active galaxies is far from conclusive. A three-prong technological assault on
the problem will, in the near future, hopefully provide new insights into the
structure of active galactic nuclei with the construction of second-generation
atmospheric Cherenkov telescopes, large-scale EeV cosmic ray detectors and high
energy neutrino telescopes.

1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg