Imaging an Event Horizon: Mitigation of Source Variability of Sagittarius A*

Abstract

The black hole in the center of the Galaxy, associated with the compact source Sagittarius A* (Sgr A*), is predicted to cast a shadow upon the emission of the surrounding plasma flow, which encodes the influence of general relativity in the strong-field regime. The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) network with a goal of imaging nearby supermassive black holes (in particular Sgr A* and M87) with angular resolution sufficient to observe strong gravity effects near the event horizon. General relativistic magnetohydrodynamic (GRMHD) simulations show that radio emission from Sgr A* exhibits vari- ability on timescales of minutes, much shorter than the duration of a typical VLBI imaging experiment, which usually takes several hours. A changing source structure during the observations, however, violates one of the basic assumptions needed for aperture synthesis in radio interferometry imaging to work. By simulating realistic EHT observations of a model movie of Sgr A*, we demonstrate that an image of the average quiescent emission, featuring the characteristic black hole shadow and photon ring predicted by general relativity, can nonetheless be obtained by observing over multiple days and subsequent processing of the visibilities (scaling, averaging, and smoothing) before imaging. Moreover, it is shown that this procedure can be combined with an existing method to mitigate the effects of interstellar scattering. Taken together, these techniques allow the black hole shadow in the Galactic center to be recovered on the reconstructed image.

10 pages, 12figures, accepted for publication in ApJ

References in corpus (7)

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Cited by in corpus (43)

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• BlackHoleCam: fundamental physics of the Galactic center
• Key Science Goals for the Next-Generation Event Horizon Telescope
• Sgr A* and General Relativity
• Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum
• Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
• Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of SAGITTARIUS A*
• Radio observations of active galactic nuclei with mm-VLBI
• Simulations of imaging the event horizon of Sagittarius A* from space
• Event Horizon Telescope Observations as Probes for Quantum Structure of Astrophysical Black Holes
• Testing General Relativity with Accretion-Flow Imaging of Sgr A*
• Dynamical Imaging with Interferometry
• Superresolution Interferometric Imaging with Sparse Modeling Using Total Squared Variation --- Application to Imaging the Black Hole Shadow
• The Effects of Accretion Flow Dynamics on the Black Hole Shadow of Sagittarius A${}^{\ast }$
• Metrics and Motivations for Earth-Space VLBI: Time-Resolving Sgr A* with the Event Horizon Telescope
• Probing the innermost accretion flow geometry of Sgr A* with Event Horizon Telescope
• Constraint on the black-hole spin of M87 from the accretion-jet model
• Silhouettes of invisible black holes
• The brightest point in accretion disk and black hole spin: implication to the image of black hole M87*
• Using space-VLBI to probe gravity around Sgr A*
• Black hole parameter estimation with synthetic Very Long Baseline Interferometry data from the ground and from space
• Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase Measurements of the Event Horizon Telescope
• Using evolutionary algorithms to model relativistic jets: Application to NGC 1052
• Testing General Relativity with the Black Hole Shadow Size and Asymmetry of Sagittarius A*: Limitations from Interstellar Scattering
• GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*
• Probing spacetime and accretion model for the Galactic Center: Comparison of Kerr and dilaton black hole shadows
• Variability in GRMHD simulations of Sgr A${}^{\ast }$: Implications for EHT closure phase observations
• Black hole Spin Measurement Based on Time-domain VLBI Observations of Infalling Gas Cloud
• MeqSilhouette : A mm-VLBI observation and signal corruption simulator
• Principal Component Analysis as a Tool for Characterizing Black Hole Images and Variability
• Event horizon silhouette: implications to supermassive black holes M87* and SgrA*
• Imaging black holes: past, present and future
• Seeing Black Holes : from the Computer to the Telescope
• MeqSilhouette v2: Spectrally-resolved polarimetric synthetic data generation for the Event Horizon Telescope
• System Design for the Event Horizon Imaging Experiment Using the PECMEO Concept
• An Event Horizon Imager (EHI) Mission Concept Utilizing Medium Earth Orbit Sub-mm Interferometry
• Time Domain Filtering of Resolved Images of Sgr A*
• Spins of supermassive black holes M87* and SgrA* revealed from the size of dark spots in Event Horizon Telescope Images
• The immediate environment of an astrophysical black hole
• On the prospects of imaging Sagittarius A* from space
• Visible shapes of black holes M87* and SgrA*