Time Domain Filtering of Resolved Images of Sgr A*

Abstract

The goal of the Event Horizon Telescope (EHT) is to provide spatially resolved images of Sgr A*, the source associated with the Galactic Center black hole. Because Sgr A* varies on timescales short compared to an EHT observing campaign, it is interesting to ask whether variability contains information about the structure and dynamics of the accretion flow. In this paper, we introduce "time-domain filtering", a technique to filter time fluctuating images with specific temporal frequency ranges, and demonstrate the power and usage of the technique by applying it to mock millimeter wavelength images of Sgr A*. The mock image data is generated from General Relativistic Magnetohydrodynamic (GRMHD) simulation and general relativistic ray-tracing method. We show that the variability on each line of sight is tightly correlated with a typical radius of emission. This is because disk emissivity fluctuates on a timescale of order the local orbital period. Time-domain filtered images therefore reflect the model dependent emission radius distribution, which is not accessible in time-averaged images. We show that, in principle, filtered data have the power to distinguish between models with different black hole spins, different disk viewing angles, and different disk orientations in the sky.

13 pages, 9 figures, accepted for publication in ApJ

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• Hot Atmospheres, Cold Gas, AGN Feedback and the Evolution of Early Type Galaxies: a Topical Perspective
• Dynamical Imaging with Interferometry
• Mass-ratio and Magnetic Flux-Dependence of Modulated Accretion from Circumbinary Disks
• Black hole Spin Measurement Based on Time-domain VLBI Observations of Infalling Gas Cloud
• Relativistic Reflection Modeling in AGN and Related Variability from PCA: A Brief Review