Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with
  ALMA   A radio source at the Galactic center Sgr A* is a prime supermassive black
hole candidate and therefore key to developing our understanding of them. Time
variations in the 230 GHz band flux of Sgr A* have been found with the Atacama
Large Millimeter/submillimeter Array (ALMA) Cycle 5 observations. Measuring the
flux density of Sgr A* in 1 min snapshots at 217.5, 219.5, and 234.0 GHz, we
obtained light curves for ten 70 min periods. The light curves show variations
at a few tens of minutes and hourly scales. The shorter timescale is similar to
the orbital period of the innermost stable circular orbit around a $4\times
10^{6}$ $M_{\odot}$ black hole, suggesting that the variation originates from
the immediate vicinity of Sgr A*. We also detected no time lag between 217.5
and 234.0 GHz and a dependence of the spectral index on the flux density.

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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
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The categories of this paper are: atom-ph
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The categories of this paper are: stat
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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: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin