Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: ALMA Observations of the Terahertz Spectrum of Sagittarius A*   We present ALMA observations at 233, 678, and 870 GHz of the Galactic Center
black hole, Sagittarius A*. These observations reveal a flat spectrum over this
frequency range with spectral index $\alpha \approx -0.3$, where the flux
density $S \propto \nu^\alpha$. We model the submm and far infrared spectrum
with a one zone synchrotron model of thermal electrons. We infer electron
densities $n = (2-5) \times 10^6$ cm$^{-3}$, electron temperatures $T_e = (1-3)
\times 10^{11}$ K, and magnetic field strength $B = 10-50$ G. The parameter
range can be further constrained using the observed quiescent X-ray luminosity.
The flat submm spectrum results in a high electron temperature and implies that
the emitting electrons are efficiently heated. We also find that the emission
is most likely optically thin at 233 GHz. These results indicate that
millimeter and submillimeter wavelength very long baseline interferometry of
Sgr A* including those of the Event Horizon Telescope should see a transparent
emission region down to event horizon scales.

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The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
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The categories of this paper are: physics
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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph