First Space-VLBI Observations of Sagittarius A*
Michael D. Johnson, Yuri Y. Kovalev, Mikhail M. Lisakov, Petr A., Voitsik, Carl R. Gwinn, and Gabriele Bruni

TL;DR
This paper reports the first Earth-space VLBI observations of Sgr A* using the RadioAstron project, achieving unprecedented resolution but not detecting fringes on longer baselines, highlighting the need for submillimeter observations.
Contribution
First space VLBI observations of Sgr A* demonstrating the potential and limitations of space VLBI at centimeter wavelengths for black hole imaging.
Findings
Consistent with anisotropic Gaussian scattering at short baselines.
Detection of persistent image substructure at intermediate baselines.
No fringes detected on long ground or space baselines.
Abstract
We report results from the first Earth-space VLBI observations of the Galactic Center supermassive black hole, Sgr A*. These observations used the space telescope Spektr-R of the RadioAstron project together with a global network of 20 ground telescopes, observing at a wavelength of 1.35cm. Spektr-R provided baselines up to 3.9 times the diameter of the Earth, corresponding to an angular resolution of approximately 55 microarcseconds and a spatial resolution of at the source, where is the Schwarzschild radius of Sgr A*. Our short ground baseline measurements (<80 M\lambda) are consistent with an anisotropic Gaussian image, while our intermediate ground baseline measurements (100-250 M\lambda) confirm the presence of persistent image substructure in Sgr A*. Both features are consistent with theoretical expectations for strong scattering in…
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