Dynamical Imaging with Interferometry

Abstract

By linking widely separated radio dishes, the technique of very long baseline interferometry (VLBI) can greatly enhance angular resolution in radio astronomy. However, at any given moment, a VLBI array only sparsely samples the information necessary to form an image. Conventional imaging techniques partially overcome this limitation by making the assumption that the observed cosmic source structure does not evolve over the duration of an observation, which enables VLBI networks to accumulate information as the Earth rotates and changes the projected array geometry. Although this assumption is appropriate for nearly all VLBI, it is almost certainly violated for submillimeter observations of the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*), which has a gravitational timescale of only ~20 seconds and exhibits intra-hour variability. To address this challenge, we develop several techniques to reconstruct dynamical images ("movies") from interferometric data. Our techniques are applicable to both single-epoch and multi-epoch variability studies, and they are suitable for exploring many different physical processes including flaring regions, stable images with small time-dependent perturbations, steady accretion dynamics, or kinematics of relativistic jets. Moreover, dynamical imaging can be used to estimate time-averaged images from time-variable data, eliminating many spurious image artifacts that arise when using standard imaging methods. We demonstrate the effectiveness of our techniques using synthetic observations of simulated black hole systems and 7mm Very Long Baseline Array observations of M87, and we show that dynamical imaging is feasible for Event Horizon Telescope observations of Sgr A*.

16 Pages, 12 Figures, Accepted for publication in ApJ

References in corpus (18)

• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei III. Kinematics of Parsec-Scale Radio Jets
• A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
• The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
• Polarimetry of near-infrared flares from Sagittarius A*
• Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope using Sparse Modeling
• Imaging the Supermassive Black Hole Shadow and Jet Base of M87 with the Event Horizon Telescope
• Super-resolution Full Polarimetric Imaging for Radio Interferometry with Sparse Modeling
• Imaging an Event Horizon: Mitigation of Scattering Toward Sagittarius A*
• The Submillimeter Polarization of Sgr A*
• ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow
• Stochastic Optics: A Scattering Mitigation Framework for Radio Interferometric Imaging
• Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase Measurements of the Event Horizon Telescope
• Observations of the Structure and Dynamics of the Inner M87 Jet
• Relative Astrometry of Compact Flaring Structures in Sgr A* with Polarimetric VLBI
• Transient Astrophysics with the Square Kilometre Array
• Time Domain Filtering of Resolved Images of Sgr A*
• Assessing the quality of restored images in optical long-baseline interferometry

Cited by in corpus (2)

• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• Black Hole Spin Signature in the Black Hole Shadow of M87 in the Flaring State