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Interferometric Imaging Directly with Closure Phases and Closure Amplitudes

Chael, Andrew A. and Johnson, Michael D. and Bouman, Katherine L. and Blackburn, Lindy L. and Akiyama, Kazunori and Narayan, Ramesh (2018) Interferometric Imaging Directly with Closure Phases and Closure Amplitudes. Astrophysical Journal, 857 (1). Art. No. 23. ISSN 1538-4357.

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Interferometric imaging now achieves angular resolutions as fine as ~10 μas, probing scales that are inaccessible to single telescopes. Traditional synthesis imaging methods require calibrated visibilities; however, interferometric calibration is challenging, especially at high frequencies. Nevertheless, most studies present only a single image of their data after a process of "self-calibration," an iterative procedure where the initial image and calibration assumptions can significantly influence the final image. We present a method for efficient interferometric imaging directly using only closure amplitudes and closure phases, which are immune to station-based calibration errors. Closure-only imaging provides results that are as noncommittal as possible and allows for reconstructing an image independently from separate amplitude and phase self-calibration. While closure-only imaging eliminates some image information (e.g., the total image flux density and the image centroid), this information can be recovered through a small number of additional constraints. We demonstrate that closure-only imaging can produce high-fidelity results, even for sparse arrays such as the Event Horizon Telescope, and that the resulting images are independent of the level of systematic amplitude error. We apply closure imaging to VLBA and ALMA data and show that it is capable of matching or exceeding the performance of traditional self-calibration and CLEAN for these data sets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Chael, Andrew A.0000-0003-2966-6220
Johnson, Michael D.0000-0002-4120-3029
Bouman, Katherine L.0000-0003-0077-4367
Blackburn, Lindy L.0000-0002-9030-642X
Akiyama, Kazunori0000-0002-9475-4254
Narayan, Ramesh0000-0002-1919-2730
Additional Information:© 2018. The American Astronomical Society. Received 2017 December 5; revised 2018 February 18; accepted 2018 March 12; published 2018 April 10. We extend particular thanks to the anonymous referee, whose suggestion of the NFFT library and unusually thorough and thoughtful comments substantially improved this work. We thank Craig Walker and Michael Janßen for their helpful conversations, comments, and suggestions. We thank Roman Gold, Monica Mościbrodzka, and Chi–Kwan Chan for providing the model images used in Section 5.1 and Svetlana Jorstad and Alan Marscher for the 43 GHz 3C273 image used in the same section. We additionally thank Craig Walker for providing the 7 mm VLBA data used in Section 5.2. We thank the National Science Foundation (AST-1440254, AST-1614868, AST-1312651) and the Gordon and Betty Moore Foundation (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. KA is financially supported by the Jansky Fellowship of the National Radio Astronomy Observatory. This study makes use of 43 GHz VLBA data from the VLBA-BU Blazar Monitoring Program (VLBA-BU-BLAZAR;, funded by NASA through the Fermi Guest Investigator Program. 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. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00015.SV. ALMA is a partnership of the ESO (representing its member states), NSF (USA), and NINS (Japan), together with the NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF-5278
John Templeton FoundationUNSPECIFIED
Jansky FellowshipUNSPECIFIED
Subject Keywords:accretion, accretion disks; black hole physics; Galaxy: center; techniques: high angular resolution; techniques: image processing
Issue or Number:1
Record Number:CaltechAUTHORS:20190405-150443709
Persistent URL:
Official Citation:Andrew A. Chael et al 2018 ApJ 857 23
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94513
Deposited By: George Porter
Deposited On:05 Apr 2019 22:30
Last Modified:03 Oct 2019 21:04

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