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

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 <sup>1

1</sup> 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 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 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 as at this frequency. The intrinsic size of Sgr A* thus appears to be Schwarzschild radii for a 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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Contents

• 1. Introduction
• 2. Observations
• 3. Data analysis and Results at 86 GHz
• 4. Data analysis at 215 GHz, Results, and Discussion
  • 4.1. Fringe Fitting
  • 4.2. Calibration and size estimate
    • 4.2.1. The flux density of the compact VLBI component
    • 4.2.2. The correlated flux density
    • 4.2.3. The source size
• 5. Summary
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
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