VLBA23A-078

Joint EHT, JWST, VLA, and VLBA+GBT Observations of Sgr A* in April 2023

Abstract

We propose three joint VLA and VLBA+GBT 7-hour tracks concurrent with the Event Horizon Telescope (EHT) multi-wavelength campaign in April 2023, the first where the James Webb Space Telescope will join. Characterizing the Sgr A*'s variability cannot be solely achieved with EHT observations and requires a view of the source across the entire multi-wavelength spectrum. Using simultaneous EHT(ALMA)/VLA/ VLBA+GBT/JWST observations, we will model the variable emission across a wide portion of the electromagnetic spectrum. Using three high-frequency VLA subarrays and the VLBA at a higher frequency, we will have the most exhaustive coverage of the flaring emission yet attempted. These data will constrain the flaring emission properties, allowing us to disentangle Sgr A*'s intrinsic variability, which is critical for obtaining high-fidelity images of the event horizon. The GBT is instrumental due to its high sensitivity, enabling detections to VLBA antennas, especially at 86 GHz. Simultaneous radio/submm observations will allow us to constrain the spectral index near the submm bump. The submillimeter bump probes the region where the quiescent emission's optical depth changes significantly and is crucial for the shadow image's interpretation. This joint VLA and VLBA+GBT proposal is part of a more extensive multi-wavelength effort spanning radio through X-rays.

Investigators

Name	Institution
Geoffrey Bower	Academia Sinica
Daryl Haggard	McGill University
Kazuhiro Hada	Istituto Nazionale di Astrofisica; National Astronomical Observatory of Japan
Sera Markoff	Amsterdam, Universiteit van
Mark Wardle	Macquarie University
Farhad Yusef-Zadeh	Northwestern University
Joseph Michail *	Northwestern University
GBT Operator	Green Bank Observatory

* indicates the PI