Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An Overview of Blazar Variability   Blazars are characterized by rapid variability at virtually all wavelengths
from radio through TeV gamma-rays. The challenge since their discovery has been
to understand the origin of their luminous, apparently nonthermal, nuclear
emission. Considerable progress has been made in recent years thanks to a
handful of multiwavelength monitoring campaigns with high enough temporal
sampling to resolve the most rapid variations. The best data for a few objects
have shown a variety of behaviors, for the most part commensurate with
synchrotron and Compton-scattered emission from a relativistic jet, though
better data for more blazars are still clearly needed. In particular, the
origin of the seed photons that are upscattered to gamma-ray energies remains
unclear. The latest multiwavelength light curves for the BL Lac object
PKS2155-304 appear to rule out synchrotron emission from a homogeneous source.

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The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: atom-ph
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The categories of this paper are: bayes-an
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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: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol