Stochastic Optics: A Scattering Mitigation Framework for Radio Interferometric Imaging

Abstract

Just as turbulence in the Earth's atmosphere can severely limit the angular resolution of optical telescopes, turbulence in the ionized interstellar medium fundamentally limits the resolution of radio telescopes. We present a scattering mitigation framework for radio imaging with very long baseline interferometry (VLBI) that partially overcomes this limitation. Our framework, "stochastic optics," derives from a simplification of strong interstellar scattering to separate small-scale ("diffractive") effects from large-scale ("refractive") effects, thereby separating deterministic and random contributions to the scattering. Stochastic optics extends traditional synthesis imaging by simultaneously reconstructing an unscattered image and its refractive perturbations. Its advantages over direct imaging come from utilizing the many deterministic properties of the scattering -- such as the time-averaged "blurring," polarization independence, and the deterministic evolution in frequency and time -- while still accounting for the stochastic image distortions on large scales. These distortions are identified in the image reconstructions through regularization by their time-averaged power spectrum. Using synthetic data, we show that this framework effectively removes the blurring from diffractive scattering while reducing the spurious image features from refractive scattering. Stochastic optics can provide significant improvements over existing scattering mitigation strategies and is especially promising for imaging the Galactic Center supermassive black hole, Sagittarius A*, with the Global mm-VLBI Array and with the Event Horizon Telescope.

12 Pages, 8 Figures, Accepted for publication in ApJ

References in corpus (18)

• Viewing the Shadow of the Black Hole at the Galactic Center
• Adaptive Optics for Astronomy
• High Resolution Linear Polarimetric Imaging for the Event Horizon Telescope
• The Intrinsic Size of Sagittarius A* from 0.35 cm to 6 cm
• 100 Microarcsecond Resolution VLBI Imaging of Anisotropic Interstellar Scattering towards Pulsar B0834+06
• The Angular Broadening of the Galactic Center Pulsar SGR J1745-29: A New Constraint on the Scattering Medium
• Modeling Seven Years of Event Horizon Telescope Observations with Radiatively Inefficient Accretion Flow Models
• Theory and Simulations of Refractive Substructure in Resolved Scatter-Broadened Images
• Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
• Imaging an Event Horizon: Mitigation of Scattering Toward Sagittarius A*
• The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*
• Multiwavelength VLBI observations of Sagittarius A*
• Discovery of Substructure in the Scatter-Broadened Image of Sgr A*
• Extreme Brightness Temperatures and Refractive Substructure in 3C273 with RadioAstron
• The Optics of Refractive Substructure
• The Intrinsic Shape of Sagittarius A* at 3.5-mm Wavelength
• Asymmetric structure in Sgr A* at 3mm from closure phase measurements with VLBA, GBT and LMT
• The microarcsecond structure of an AGN jet via interstellar scintillation

Cited by in corpus (40)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• Interferometric Imaging Directly with Closure Phases and Closure Amplitudes
• Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope using Sparse Modeling
• Testing General Relativity with the Event Horizon Telescope
• Key Science Goals for the Next-Generation Event Horizon Telescope
• The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
• The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
• Evaluation of New Submillimeter VLBI Sites for the Event Horizon Telescope
• 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
• Dynamical Imaging with Interferometry
• The ALMA Phasing System: A Beamforming Capability for Ultra-High-Resolution Science at (Sub)Millimeter Wavelengths
• Superresolution Interferometric Imaging with Sparse Modeling Using Total Squared Variation --- Application to Imaging the Black Hole Shadow
• Metrics and Motivations for Earth-Space VLBI: Time-Resolving Sgr A* with the Event Horizon Telescope
• The Black Hole Explorer: Photon Ring Science, Detection and Shape Measurement
• Using space-VLBI to probe gravity around Sgr A*
• First Very Long Baseline Interferometry Detections at 870μm
• Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase Measurements of the Event Horizon Telescope
• Testing General Relativity with the Black Hole Shadow Size and Asymmetry of Sagittarius A*: Limitations from Interstellar Scattering
• Demonstrating Photon Ring Existence with Single-Baseline Polarimetry
• The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm
• Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86 GHz
• Polarization images of accretion flow around supermassive black holes: imprints of toroidal field structure
• A Characterization of the ALMA Phasing System at 345 GHz
• How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models
• MeqSilhouette v2: Spectrally-resolved polarimetric synthetic data generation for the Event Horizon Telescope
• VLBI imaging of black holes via second moment regularization
• First Space-VLBI Observations of Sagittarius A*
• Substructure of visibility functions from scattered radio emission of pulsars through space VLBI
• Multi-wavelength torus-jet model for Sgr~A*
• Measuring Black Hole Light Echoes with Very Long Baseline Interferometry
• Probing Accretion Turbulence in the Galactic Center with EHT Polarimetry
• Impact of the nonthermal electron radiation effects on the horizon scale image structure of Sagittarius A*
• The Core-shift of Sagittarius A* as a Discriminant between Disk and Jet Emission Models with millimeter-VLBI
• Multiobjective optimization for scattering mitigation and scattering screen reconstruction in VLBI observations of the Galactic Center
• Diagnosing Turbulence in the Neutral and Molecular Interstellar Medium of Galaxies
• Direct VLBI Detection of Interstellar Turbulence Imprint on a Quasar: TXS 2005+403
• Orbit design for mitigating interstellar scattering effects in Earth-space VLBI observations of Sgr A*