VLBA21B-371

Simultaneous 86 GHz VLBA+GBT and EHT Observations in March 2022

Abstract

We propose three simultaneous VLBA+GBT 7-hour concurrent tracks with EHT and VLA observations of Sgr A* in March 2022. The characterization of the variability and emission mechanism in Sgr A* cannot be solely achieved with EHT observations and requires a view of the source across the entire multi-wavelength spectrum. A large multi-wavelength campaign has been planned for the EHT 2022 observing window, from radio to X-ray wavelengths. However, there is a gap in frequency coverage in the radio at 86 GHz, which is of great interest due to its insight into the accretion flow of Sgr A* and non-dominant interstellar scattering. The GBT is instrumental to this proposal due to its high sensitivity, enabling polarization measurements and detections to VLBA antennas. We will combine these observations with previously approved lower-frequency VLA data and higher frequency ALMA data to determine the SED of the quiescent emission in Sgr A* and constrain the spectral index near the "submillimeter bump." The bump probes emission where the accretion flow's optical depth changes significantly from thick to thin and is critical to interpreting near-horizon images with the EHT. These data are high-risk, high-reward as any flares will be simultaneously observed across the entire electromagnetic spectrum.

Investigators

Name	Institution
GBT Operator	Green Bank Observatory
Venkatessh Ramakrishnan	Turku, University of
Thomas Krichbaum	Max-Planck-Institut für Radioastronomie
Daryl Haggard	McGill University
Kazuhiro Hada	Istituto Nazionale di Astrofisica; National Astronomical Observatory of Japan ; Nagoya City University
Sera Markoff	Amsterdam, Universiteit van
Geoffrey Bower	Academia Sinica
Sara Issaoun	Center for Astrophysics | Harvard & Smithsonian; Nijmegen, Radboud Universiteit
Mark Wardle	Macquarie University
Farhad Yusef-Zadeh	Northwestern University
Joseph Michail *	Center for Astrophysics | Harvard & Smithsonian

* indicates the PI