Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High brightness temperatures and circular polarisation in extra-galactic
  radio sources   Some rapidly variable extra-galactic radio sources show very high brightness
temperatures T_B>10^{12}K and high degrees of circular polarisation (1%).
Standard synchrotron models that assume a power-law electron distribution
cannot produce such high temperatures and have much lower degrees of intrinsic
circular polarisation. We examine the synchrotron and inverse Compton radiation
from a monoenergetic electron distribution using standard synchrotron theory.
Constraints on the source parameters are found by formulating the results as
functions of the source size, Doppler boosting factor, optical depth to
synchrotron self-absorption, maximum frequency of synchrotron emission, and the
strength of the inverse Compton radiation. The model gives brightness
temperatures T_B=10^{13}K to 10^{14}K for moderate (<10) Doppler boosting
factors and intrinsic degrees of circular polarisation at the percent level. It
predicts a spectrum I_\nu\propto\nu^{1/3} between the radio and the infra-red
as well as emission in the MeV to GeV range. We find the conditions under which
electrons do not cool within the source, enabling the GHz emission to emerge
without absorption and the potentially catastrophic energy losses by inverse
Compton scattering to be avoided. We suggest that sources such as PKS 1519
-273, PKS 0405 -385 and J 1819 +3845 can be understood within this scenario
without invoking high Doppler boosting factors, coherent emission mechanisms,
or the dominance of proton synchrotron radiation.

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The categories of this paper are: cmp-lg
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: physics
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: stat
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The categories of this paper are: hep-th
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The categories of this paper are: cs
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The categories of this paper are: eess
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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: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys