7 MILLIMETER VLBA OBSERVATIONS OF SAGITTARIUS-A-ASTERISK

We present 7 mm Very Long Baseline Array observations of the compact n onthermal radio source in the Galactic center; Sagittarius A. These o bservations confirm the hypothesis that the image of Sgr A:: is a res olved elliptical Gaussian caused by the scattering of an intervening t hermal plasma. The measured major axis of Sgr A is 0.76 +/- 0.04 mas, consistent with the predicted scattering size of 0.67 +/- 0.03. We fi nd an axial ratio of 0.73 +/- 0.10 and a position angle of 77 degrees. 0 +/- 7 degrees.4. These results are fully consistent with VLBI observ ations at longer wavelengths and at 3 mm. We find no evidence for any additional compact structure to a limit of 35 mJy. The underlying radi o source must be smaller than 4.1 AU for a Galactocentric distance of 8.5 kpc. This result is consistent with the conclusion that the radio emission from Sgr A results from synchrotron or cyclo-synchrotron rad iation of gas in the vicinity of a black hole with a mass near 10(6) M o-..