VLBI imaging of black holes via second moment regularization

Abstract

The imaging fidelity of the Event Horizon Telescope (EHT) is currently determined by its sparse baseline coverage. In particular, EHT coverage is dominated by long baselines, and is highly sensitive to atmospheric conditions and loss of sites between experiments. The limited short/mid-range baselines especially affect the imaging process, hindering the recovery of more extended features in the image. We present an algorithmic contingency for the absence of well-constrained short baselines in the imaging of compact sources, such as the supermassive black holes observed with the EHT. This technique enforces a specific second moment on the reconstructed image in the form of a size constraint, which corresponds to the curvature of the measured visibility function at zero baseline. The method enables the recovery of information lost in gaps of the baseline coverage on short baselines and enables corrections of any systematic amplitude offsets for the stations giving short-baseline measurements present in the observation. The regularization can use historical source size measurements to constrain the second moment of the reconstructed image to match the observed size. We additionally show that a characteristic size can be derived from available short-baseline measurements, extrapolated from other wavelengths, or estimated without complementary size constraints with parameter searches. We demonstrate the capabilities of this method for both static and movie reconstructions of variable sources.

arXiv comment14 pages, 11 figures; accepted for publication in A&A

References in corpus (36)

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• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• Evidence for Low Black Hole Spin and Physically Motivated Accretion Models from Millimeter VLBI Observations of Sagittarius A*
• Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope using Sparse Modeling
• The Intrinsic Size of Sagittarius A* from 0.35 cm to 6 cm
• Methods for detecting flaring structures in Sagittarius A* with high frequency VLBI
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• Dynamical Imaging with Interferometry
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Cited by in corpus (8)

• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• Event Horizon Telescope observations of the jet launching and collimation in Centaurus A
• Multi-frequency Black Hole Imaging for the Next-Generation Event Horizon Telescope
• Demonstrating Photon Ring Existence with Single-Baseline Polarimetry
• Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86 GHz
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Expanding Sgr A* dynamical imaging capabilities with an African extension to the Event Horizon Telescope
• Imaging the event horizon of M87* from space on different timescales