2018ApJ...865..104J

Radio images of the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*), are dominated by interstellar scattering. Previous studies of Sgr A* have adopted an anisotropic Gaussian model for both the intrinsic source and the scattering, and they have extrapolated the scattering using a purely λ² scaling to estimate intrinsic properties. However, physically motivated source and scattering models break all three of these assumptions. They also predict that refractive scattering effects will be significant, which have been ignored in standard model fitting procedures. We analyze radio observations of Sgr A* using a physically motivated scattering model, and we develop a prescription to incorporate refractive scattering uncertainties when model fitting. We show that an anisotropic Gaussian scattering kernel is an excellent approximation for Sgr A* at wavelengths longer than 1 cm, with an angular size of (1.380±0.013)λ_cm²mas along the major axis, (0.703±0.013)λ_cm²mas along the minor axis, and a position angle of 81○ / . 9±0○ / . 2. We estimate that the turbulent dissipation scale is at least 600 km, with tentative support for r_in = 800 ± 200 km, suggesting that the ion Larmor radius defines the dissipation scale. We find that the power-law index for density fluctuations in the scattering material is β < 3.47, shallower than expected for a Kolmogorov spectrum (β = 11/3), and we estimate β=3.38_–0.04^+0.08 in the case of r_in = 800 km. We find that the intrinsic structure of Sgr A* is nearly isotropic over wavelengths from 1.3 mm to 1.3 cm, with a size that is roughly proportional to wavelength: θ_src∼(0.4mas)×λ_cm. We discuss implications for models of Sgr A*, for theories of interstellar turbulence, and for imaging Sgr A* with the Event Horizon Telescope.