High-resolution 86 GHz VLBA imaging of Sgr A

We present the first VLBI image of Sgr A* ever made at 86 GHz. The image shows an elliptical Gaussian brightness distribution with the same East-West elongation as seen at lower frequencies. The fitted apparent source structure is 0.21(-<0.01)(+0.02) mas by 0.13(->0.13)(+0.05) mas with a position angle of 79degrees(-33degrees)(+12degrees). The large error bar in the fitted minor axis size is mainly due to the poor spatial resolution along the North-South direction. The major axis size, however, is well determined. The discrepancy between the measured major axis size and that predicted by the current scattering angle of 0.175 mas at 86 GHz implies an intrinsic size along E-W of 0.116 mas, or, 0.93 AU at the distance of 8 kpc to the Galactic Center