VLBI Observations of the Galactic Center Source Sgr A* at 86 GHz and 215 GHz

Abstract

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.