Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The brightness temperature problem in extreme IDV quasars: a model for
  PKS 0405-385   I re-examine the brightness temperature problem in PKS 0405-385 which is an
extreme intra-day variable radio quasar with an inferred brightness temperature
of $\sim 5 \times 10^{14}$ K at 5 GHz, well above the Compton catastrophe limit
of $\sim 10^{11}$ K reached when the synchrotron photon energy density exceeds
the energy density of the magnetic field. If one takes into account the
uncertainty in the distance to the ionized clouds responsible for interstellar
scintillation causing rapid intra-day variability in PKS 0405-385 it is
possible that the brightness temperature could be as low as $\sim 10^{13}$ K at
5 GHz, or even lower. The radio spectrum can be fitted by optically thin
emission from mono-energetic electrons, or an electron spectrum with a
low-energy cut-off such that the critical frequency of the lowest energy
electrons is above the radio frequencies of interest. If one observes optically
thin emission along a long narrow emission region, the average energy density
in the emission region can be many orders of magnitude lower than calculated
from the observed intensity if one assumed a spherical emission region. I
discuss the physical conditions in the emission region and find that the
Compton catastrophe can then be avoided using a reasonable Doppler factor. I
also show that MeV to 100 GeV gamma-ray emission at observable flux levels
should be expected from extreme intra-day variable sources such as PKS
0405-385.

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The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
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The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg