Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: VLBI Observations of the Galactic Center Source Sgr A* at 86 GHz and 215
  GHz   We summarize previous VLBI observations of Sgr A* at millimeter wavelengths
and present new results from VLBI observations at 86 and at 215 GHz. At 86 GHz
the measured closure phase is close to zero, consistent with a point-like or
symmetric structure of 190 +/- 30 micro-arcsec size. At 215 GHz we have
detected Sgr A* with a signal-to-noise ratio of 6. This yields a tentative size
estimate of 50 < theta < 190 micro-arcsec, which is larger than the scattering
size of 20 micro-arcsec at this frequency. The intrinsic size of Sgr A* thus
appears to be a few up to a few ten Schwarzschild radii.

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The categories of this paper are: cond-mat
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The categories of this paper are: econ
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: quant-ph