Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Resolving the innermost parsec of Centaurus A at mid-infrared
  wavelengths   We report the results of interferometric observations of Centaurus A with the
MID-infrared Interferometer (MIDI) at ESO's VLTI telescope array. The
interferometric measurements are spectrally resolved (R = 30) in the wavelength
range 8 to 13 micron. Their spatial resolution reaches 15 mas at the shortest
wavelengths. Supplementary observations were obtained in the near-infrared with
the adaptive optics instrument NACO, and at mm wavelengths with SEST and JCMT.
We find that he mid-infrared emission from the core of Centaurus A is dominated
by an unresolved point source (<10 mas). Observations with baselines orientated
perpendicular to the radio jet reveal an extended component which can be
interpreted as a geometrically thin, dusty disk, the axis of which is aligned
with the radio jet. Its diameter is about 0.6 pc. We argue, that the unresolved
emission is dominated by a synchrotron source. Its overall spectrum is
characterized by a \nu^{-0.36} power-law which cuts off exponentially towards
high frequencies at 8x10^{13} Hz and becomes optically thick at \nu < 45 GHz.
Based on a Synchrotron Self Compton (SSC) interpretation for the gamma-ray
emission, we find a magnetic field strength of 26 microTesla and a maximum
energy of relativistic electrons of \gamma_c = E_c/m_e c^2 = 8500. Near
\gamma_c, the acceleration time scale is 4 days, in good agreement with the
fastest X-ray variations. Our SSC model argues for an upper limit for the bulk
Lorentz factor < 2.5, at variance with the concept of a "mis-directed BL Lac
object". We estimate a thermal core luminosity of 1.3x10^{34} W, intermediate
between the values for highly efficiently accreting AGN (e.g. Seyfert galaxies)
and those of typical FR I radio galaxies.

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The categories of this paper are: chao-dyn
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The categories of this paper are: math
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: adap-org
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: q-alg