Variability in GRMHD simulations of Sgr A$^*$: Implications for EHT closure phase observations

Understand

The observable quantities that carry the most information regarding the structures of the images of black holes in the interferometric observations with the Event Horizon Telescope are the closure phases along different baseline triangles.

• We use long time span, high cadence, GRMHD+radiative transfer models of Sgr A$^*$ to investigate the expected variability of closure phases in such observations.
• We find that, in general, closure phases along small baseline triangles show little variability, except in the cases when one of the triangle vertices crosses one of a small regions of low visibility amplitude.
• The closure phase variability increases with the size of the baseline triangle, as larger baselines probe the small-scale structures of the images, which are highly variable.