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Astron. Astrophys. 335, L106-L110 (1998)

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Letter to the Editor

VLBI observations of the galactic center source Sgr A* at 86 GHz and 215 GHz

T.P. , Krichbaum 1, D.A. , Graham 1, A. , Witzel 1, A. , Greve 2, J.E. , Wink 2, M. , Grewing 2, F. , Colomer 3, P. , de Vicente 3, J. , Gómez-González 3, A. , Baudry 4, J.A. and Zensus 1

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Institut de Radioastronomie Millimétrique, F-38406 St. Martin d'Hères, France
3 Centro Astronómico de Yebes, Apartado 148, E-19080 Guadalajara, Spain
4 Observatoire de Bordeaux, B.P. 89, F-33270 Floirac, France

Received 17 April 1998 / Accepted 8 May 1998

Abstract

We have observed and detected Sgr A* with VLBI at 86 GHz and at 215 GHz in March 1995. At 86 GHz the measured closure phase is close to zero, consistent with a point-like or symmetric structure of [FORMULA] µas in size. At 215 GHz we have detected Sgr A* with a signal-to-noise ratio of 6. This yields a tentative size estimate of [FORMULA] µas which, despite of a limited calibration accuracy and uncertainty in the origin of the mm/sub-mm total flux density excess, lies well above the scattering size of [FORMULA]as at this frequency. The intrinsic size of Sgr A* thus appears to be [FORMULA] Schwarzschild radii for a [FORMULA] [FORMULA] black hole.

Key words: Galaxy: center – galaxies: individual: Sgr A* – scattering – techniques: interferometry – galaxies: nuclei

Send offprint requests to: T.P. Krichbaum

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
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