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High-resolution Linear Polarimetric Imaging for the Event Horizon Telescope

Chael, Andrew A. and Johnson, Michael D. and Narayan, Ramesh and Doeleman, Sheperd S. and Wardle, John F. C. and Bouman, Katherine L. (2016) High-resolution Linear Polarimetric Imaging for the Event Horizon Telescope. Astrophysical Journal, 829 (1). Art. No. 11. ISSN 1538-4357. doi:10.3847/0004-637x/829/1/11.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Chael, Andrew A.0000-0003-2966-6220
Johnson, Michael D.0000-0002-4120-3029
Narayan, Ramesh0000-0002-1919-2730
Doeleman, Sheperd S.0000-0002-9031-0904
Bouman, Katherine L.0000-0003-0077-4367
Additional Information:© 2016. The American Astronomical Society. Received 2015 December 4; revised 2016 June 8; accepted 2016 July 6; published 2016 September 14. We thank the National Science Foundation (AST-1310896, AST-1312034, AST-1211539, and AST-1440254) and the Gordon and Betty Moore Foundation (#GBMF-3561) for financial support of this work. R.N.'s research was supported in part by NSF grant AST1312651 and NASA grant TCAN NNX14AB47G. K.B. was supported by NSF CGV-1111415 and a NSF Graduate Fellowship. We thank Svetlana Jorstad, Alan Marscher, and Kazuhiro Hada for providing the data imaged in Section 5.2 and for their helpful comments. We thank Avery Broderick, Jason Dexter, and Roman Gold for generously providing model images. We also thank Lindy Blackburn for his help on simulating gain and phase errors and Kazunori Akiyama for his suggestion of applying total variation as a polarimetric regularizer. We thank the anonymous referee, whose thorough suggestions significantly improved this paper. 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 an instrument of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation that is operated by Associated Universities, Inc.
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF-3561
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:black hole physics; Galaxy: center; techniques: high angular resolution; techniques: image processing; techniques: interferometric
Issue or Number:1
Record Number:CaltechAUTHORS:20190405-150444073
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Official Citation:Andrew A. Chael et al 2016 ApJ 829 11
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94516
Deposited By: George Porter
Deposited On:05 Apr 2019 22:53
Last Modified:16 Nov 2021 17:05

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