The structure of radio sources 3C 273B and 3C 84 deduced from the 'closure' phases and visibility amplitudes observed with three-element interferometers

Rogers, A. E. E.; Hinteregger, H. F.; Whitney, A. R.; Counselman, C. C.; Shapiro, I. I.; Wittels, J. J.; Klemperer, W. K.; Warnock, W. W.; Clark, T. A.; Hutton, Laura

doi:10.1086/153162

Cited by 130 publications

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“…However, adding the phases observed on three baselines around a triangle cancels the atmospheric contribution at each station, so these closure phases only contain information about the source. Assuming that the visibility amplitudes can be calibrated to remove station-dependent gain terms (which vary more slowly than the unstable phase terms from the atmosphere), calibrated amplitudes can be combined with closure phases in the bispectrum, the product of three simultaneous visibilities around a triangle (Rogers et al 1974), (TMS),˜˜˜(…”

Section: Fundamentals Of Interferometric Imagingmentioning

confidence: 99%

High-Resolution Linear Polarimetric Imaging for the Event Horizon Telescope

Chael

Johnson

Narayan

et al. 2016

ApJ

231

318

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Images of the linear polarizations of synchrotron radiation around active galactic nuclei (AGNs) highlight their projected magnetic field lines and provide key data for understanding the physics of accretion and outflow from supermassive black holes. The highest-resolution polarimetric images of AGNs are produced with Very Long Baseline Interferometry (VLBI). Because VLBI incompletely samples the Fourier transform of the source image, any image reconstruction that fills in unmeasured spatial frequencies will not be unique and reconstruction algorithms are required. In this paper, we explore some extensions of the Maximum Entropy Method (MEM) to linear polarimetric VLBI imaging. In contrast to previous work, our polarimetric MEM algorithm combines a Stokes I imager that only uses bispectrum measurements that are immune to atmospheric phase corruption, with a joint Stokes Q and U imager that operates on robust polarimetric ratios. We demonstrate the effectiveness of our technique on 7 and 3 mm wavelength quasar observations from the VLBA and simulated 1.3 mm Event Horizon Telescope observations of Sgr A * and M87. Consistent with past studies, we find that polarimetric MEM can produce superior resolution compared to the standard CLEAN algorithm, when imaging smooth and compact source distributions. As an imaging framework, MEM is highly adaptable, allowing a range of constraints on polarization structure. Polarimetric MEM is thus an attractive choice for image reconstruction with the EHT.

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Section: Fundamentals Of Interferometric Imagingmentioning

confidence: 99%

High-Resolution Linear Polarimetric Imaging for the Event Horizon Telescope

Chael

Johnson

Narayan

et al. 2016

ApJ

231

318

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“…However, closure quantities are robust observables and can therefore be used for model fitting even when baseline-based visibilities are contaminated with station-based phase and gain errors. Indeed, closure quantities have been successfully used for model fitting (e.g., Rogers et al 1974), including recent experiments to place limits on the apparent size and structure of Sgr A* at wavelengths as short as 3 mm (Doeleman et al 2001;Bower et al 2004;Shen et al 2005;Markoff et al 2007).…”

Section: Techniquesmentioning

confidence: 99%

Detecting Flaring Structures in Sagittarius A* With High-Frequency Vlbi

Doeleman

Fish

Broderick

et al. 2009

ApJ

143

167

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The super-massive black hole candidate, Sagittarius A*, exhibits variability from radio to X-ray wavelengths on timescales that correspond to < 10 Schwarzschild radii. We survey the potential of millimeter wavelength very long baseline interferometry (VLBI) to detect and constrain time-variable structures that could give rise to such variations, focusing on a model in which an orbiting hot spot is embedded in an accretion disk. Nonimaging algorithms are developed that use interferometric closure quantities to test for periodicity, and applied to an ensemble of hot spot models that sample a range of parameter space. We find that structural periodicity in a wide range of cases can be detected on most potential VLBI arrays using modern VLBI instrumentation. Future enhancements of millimeter/submillimeter VLBI arrays including phased-array processors to aggregate VLBI station collecting area, increased bandwidth recording, and addition of new VLBI sites all significantly aid periodicity detection. The methods described herein can be applied to other models of Sagittarius A*, including jet outflows and magnetohydrodynamic accretion simulations.

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“…It is known that the closure phase is free from antenna-based phase errors (Jennison 1958), which can be seen from the following definition of the closure phase, , known as the bispectrum. 17 Closure phases have been used to calibrate visibility phases in VLBI observations (e.g., Rogers et al 1974).…”

Section: A Brief Introduction Of the Closure Phasementioning

confidence: 99%

Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope Using Sparse Modeling

Akiyama

Kuramochi

Ikeda

et al. 2017

ApJ

144

129

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We propose a new imaging technique for radio and optical/infrared interferometry. The proposed technique reconstructs the image from the visibility amplitude and closure phase, which are standard data products of shortmillimeter very long baseline interferometers such as the Event Horizon Telescope (EHT) and optical/infrared interferometers, by utilizing two regularization functions: the ℓ 1 -norm and total variation (TV) of the brightness distribution. In the proposed method, optimal regularization parameters, which represent the sparseness and effective spatial resolution of the image, are derived from data themselves using cross-validation (CV). As an application of this technique, we present simulated observations of M87 with the EHT based on four physically motivated models. We confirm that ℓ 1 +TV regularization can achieve an optimal resolution of ∼20%-30% of the diffraction limit λ/D max , which is the nominal spatial resolution of a radio interferometer. With the proposed technique, the EHT can robustly and reasonably achieve super-resolution sufficient to clearly resolve the black hole shadow. These results make it promising for the EHT to provide an unprecedented view of the event-horizon-scale structure in the vicinity of the supermassive black hole in M87 and also the Galactic center Sgr A * .

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The structure of radio sources 3C 273B and 3C 84 deduced from the 'closure' phases and visibility amplitudes observed with three-element interferometers

Cited by 130 publications

References 0 publications

High-Resolution Linear Polarimetric Imaging for the Event Horizon Telescope

High-Resolution Linear Polarimetric Imaging for the Event Horizon Telescope

Detecting Flaring Structures in Sagittarius A* With High-Frequency Vlbi

Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope Using Sparse Modeling

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