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Dynamical Imaging with Interferometry

Johnson, Michael D. and Bouman, Katherine L. and Blackburn, Lindy and Chael, Andrew A. and Rosen, Julian and Shiokawa, Hotaka and Roelofs, Freek and Akiyama, Kazunori and Fish, Vincent L. and Doeleman, Sheperd S. (2017) Dynamical Imaging with Interferometry. Astrophysical Journal, 850 (2). Art. No. 172. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20190405-150443824

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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 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 $\sim 20$ s and exhibits intrahour 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 multiepoch 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 7 mm Very Long Baseline Array observations of M87, and we show that dynamical imaging is feasible for Event Horizon Telescope observations of Sgr A*.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/aa97ddDOIArticle
https://arxiv.org/abs/1711.01286arXivDiscussion Paper
ORCID:
AuthorORCID
Johnson, Michael D.0000-0002-4120-3029
Bouman, Katherine L.0000-0003-0077-4367
Blackburn, Lindy0000-0002-9030-642X
Chael, Andrew A.0000-0003-2966-6220
Rosen, Julian0000-0003-1086-3224
Shiokawa, Hotaka0000-0002-8847-5275
Roelofs, Freek0000-0001-5461-3687
Akiyama, Kazunori0000-0002-9475-4254
Fish, Vincent L.0000-0002-7128-9345
Doeleman, Sheperd S.0000-0002-9031-0904
Additional Information:© 2017. The American Astronomical Society. Received 2017 July 30; revised 2017 October 27; accepted 2017 October 31; published 2017 November 30. We are particularly indebted to Craig Walker for sharing his calibrated M87 data and images and for many illuminating discussions. We gratefully acknowledge helpful conversations with John Wardle, James Guillochon, and Maciek Wielgus. We also thank Alan Marscher, Svetlana Jorstad, Dan Homan, and Matt Lister for making their multiepoch VLBI studies available to help refine and test our code. We thank Avery Broderick for providing the hot spot simulations used in this work. We thank the referee for suggesting the application of this technique to wide-field imaging studies with next-generation arrays. We thank the National Science Foundation (AST-1440254, AST-1614868) and the Gordon and Betty Moore Foundation (GBMF-3561, GBMF-5278) for financial support of this work. This work was supported in part by the black hole Initiative at Harvard University, which is supported by a grant from the John Templeton Foundation. F.R. is supported by the ERC Synergy Grant "BlackHoleCam" (Grant 610058). K.A. is financially supported by the program of Postdoctoral Fellowships for Research Abroad at the Japan Society for the Promotion of Science (JSPS). The VLBA is operated by the Long Baseline Observatory. The Long Baseline Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Funders:
Funding AgencyGrant Number
NSFAST-1440254
NSFAST-1614868
Gordon and Betty Moore FoundationGBMF-3561
Gordon and Betty Moore FoundationGBMF-5278
John Templeton FoundationUNSPECIFIED
European Research Council (ERC)610058
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
Subject Keywords:accretion, accretion disks; black hole physics; Galaxy: center; techniques: high angular resolution; techniques: interferometric
Issue or Number:2
Record Number:CaltechAUTHORS:20190405-150443824
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190405-150443824
Official Citation:Michael D. Johnson et al 2017 ApJ 850 172
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94514
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:05 Apr 2019 22:39
Last Modified:03 Oct 2019 21:04

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