Work

Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk Via Lagged Interferometric Covariance

Year: 2015

Type: article

Abstract: We show that interferometry can be applied to study irregular, rapidly rotating structures, as are expected in the turbulent accretion flow near a black hole. Specifically, we analyze the lagged covariance between interferometric baselines of similar lengths but slightly different orientations. For a flow viewed close to face-on, we demonstrate that the peak in the lagged covariance indicates the direction and angular velocity of the emission pattern from the flow. Even for moderately inclined flows, the covariance robustly estimates the flow direction, although the estimated angular velocity can be significantly biased. Importantly, measuring the direction of the flow as clockwise or counterclockwise on the sky breaks a degeneracy in accretion disk inclinations when analyzing time-averaged images alone. We explore the potential efficacy of our technique using three-dimensional, general relativistic magnetohydrodynamic simulations, and we highlight several baseline pairs for the Event Horizon Telescope (EHT) that are well-suited to this application. These results indicate that the EHT may be capable of estimating the direction and angular velocity of the emitting material near Sgr A*, and they suggest that a rotating flow may even be utilized to improve imaging capabilities.

Source: The Astrophysical Journal

DOI: 10.1088/0004-637x/813/2/132

Authors: Michael D. Johnson, Abraham Loeb, Hotaka Shiokawa, Andrew A. Chael, Sheperd S. Doeleman

Institutions: Center for Astrophysics Harvard & Smithsonian, Johns Hopkins University, Massachusetts Institute of Technology

Language: English

Topic: Astrophysical Phenomena and Observations

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: bronze

Funders: National Science Foundation, Gordon and Betty Moore Foundation

Awards: Precision Measurements of the Black-Hole Properties in the Center of the Milky Way, The Event Horizon Telescope Experiment, Building the Event Horizon Telescope: Observing Black Holes with Schwarzschild Radius Resolution, G5754899719, Spatially Resolving the Black Hole Event Horizon: (sub)mm VLBI of SgrA* and M87