ABSTRACT

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ABSTRACT: We present 7 mm lambda VLBA observations of the compact nonthermal radio source in the Galactic Center, Sgr A*. These observations confirm the hypothesis that the image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of an intervening thermal with the predicted scattering size of 0.67 +/- 0.03. We find an axial ratio of 0.73 +/- 0.10 and a position angle of 77.0 +/- 7.4 degrees. These results are fully consistent with VLBI observations at longer wavelengths and at 3 mm lambda . We find no evidence for any additional compact structure to a limit of 35 mJy. The underlying radio 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 radiation of gas in the vicinity of a black hole with a mass near 10⁶ M_\sun. We also present recent results from the BIMA array and the VLA on the polarization of Sgr A* at 4.8 and 86 GHz. At 4.8 GHz, we find an upper limit to the linear polarization of 0.1%. At 86 GHz, we find p=1+/- 1 %. We discuss interstellar propagation effects and the predictions of different models.