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S.S. Doeleman (MIT-Haystack Observatory, Westford, MA.), Z.-Q. Shen (National Astronomical Obs., Japan & ASIAA, Taiwan), A.E.E. Rogers (MIT-Haystack Observatory, Westford, MA.), G.C. Bower (NRAO, Socorro, NM.), M.C.H. Wright (U. California Berkeley), J.-H. Zhao (CfA, Cambridge, MA.), D.C. Backer (U. California Berkeley), J.W. Crowley (MIT-Haystack Observatory, Westford, MA.), R.W. Freund (NRAO, Tucson, AZ.), P.T.P. Ho (CfA, Cambridge, MA.), K.Y. Lo (ASIAA, Taiwan), D.P. Woody (Cal. Tech., OVRO, Big Pine, CA.)
At radio wavelengths, VLBI images of the compact radio source Sagittarius A* (Sgr A*) in the Galactic Center are scatter broadened with a \lambda2 dependence due to an intervening ionized medium. High frequency VLBI is the only technique available to see through this scattering and search for the intrinsic structure of Sgr A*. We present total intensity VLBI observations of Sgr A* at 86 GHz using a six station array including the VLBA antennas at Pie Town, Fort Davis and Los Alamos, the 12m antenna at Kitt Peak and the millimeter arrays at Hat Creek and Owens Valley. To avoid systematic errors due to imperfect antenna calibration, the data were modeled using interferometric closure information. The data are best modeled by a circular Gaussian brightness distribution of FWHM 0.18 ±0.02 mas (30R\mbox{sch} for a 2.6\times106M\odot Black Hole). The data are also shown to be consistent with an elliptical model corresponding to the scattering of a point source. The source structure in the N-S direction, which is less well determined than in the E-W direction due to the limited N-S (u,v) coverage of the array, is constrained to be less than 0.27 mas (45R\mbox{sch}) by these measurements. These results are marginally consistent with reasonable extrapolations of intrinsic structure estimates obtained with VLBI at 7mm wavelength.
The author(s) of this abstract have provided an email address for comments about the abstract: dole@haystack.mit.edu