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

Kazunori AkiyamaBlack Hole Initiative, Harvard University, 20 Garden Street,Cambridge, MA 02138,USAKazuki KuramochiDepartment of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JapanShiro IkedaDepartment of Statistical Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies, 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, JapanVincent L. FishMassachusetts Institute of Technology, Haystack Observatory, Route 40, Westford, MA 01886, USA; [email protected]Fumie TazakiMizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanMareki HonmaDepartment of Astronomical Science, School of Physical Sciences, Graduate University for Advanced Studies, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanSheperd S. DoelemanBlack Hole Initiative, Harvard University, 20 Garden Street,Cambridge, MA 02138,USAAvery E. BroderickDepartment of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2l 3G1, CanadaJason DexterMax Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, D-85748 Garching, GermanyMonika MościbrodzkaDepartment of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The NetherlandsKatherine L. BoumanMassachusetts Institute of Technology, Computer Science and Artificial Intelligence Laboratory, 32 Vassar Street, Cambridge, MA 02139, USAAndrew ChaelBlack Hole Initiative, Harvard University, 20 Garden Street,Cambridge, MA 02138,USAMasamichi ZaizenDepartment of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

2017en

ABI

Annotatsiya

Abstract 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 short-millimeter 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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DOI: 10.3847/1538-4357/aa6305

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