<figure><img src="image_41.png" /></figure>

**Figure 35.** Comparison of D-terms estimated with GPCAL with and without instrumental polarization self-calibration. The D-term averages estimated with the imaging pipelines on the 2017 April 11 M87 data are shown on the x-axis. The GPCAL results with (filled circles) and without (open squares) instrumental polarization self-calibration are shown on the y-axis (see the text for more details). The left, middle, and right panels show the results for M87 on 2017 April 11, J1924–2914 on 2017 April 11, and NRAO 530 on 2017 April 7, respectively. The $L_1$ norms do not change much with instrumental polarization self-calibration for M87, while they are significantly improved for the calibrators, especially for J1924–2914. This indicates that the similarity approximation employed by polsolve and LPCAL for the D-term estimation from M87 (Section 4.2) is reasonable. The calibrators may have complex linear polarization structure and D-term estimation from those sources can be improved with instrumental polarization self-calibration.

similarity approximation only. The $L_1$ norms improve from 9.2% to 1.4% and 2.9% to 2.0% for J1924–2914 and NRAO 530, respectively, with the instrumental polarization self-calibration. This result indicates that the linearly polarized structures of the calibrators are complex and cannot be easily modeled with the similarity approximation.

## ORCID iDs

Kazunori Akiyama https://orcid.org/0000-0002-9475-4254

Juan Carlos Algaba https://orcid.org/0000-0001-6993-1696

Antxon Alberdi https://orcid.org/0000-0002-9371-1033

Richard Anantua https://orcid.org/0000-0003-3457-7660

Rebecca Azulay https://orcid.org/0000-0002-2200-5393

Anne-Kathrin Baczko https://orcid.org/0000-0003-3090-3975

Mislav Baloković https://orcid.org/0000-0003-0476-6647

John Barrett https://orcid.org/0000-0002-9290-0764

Bradford A. Benson https://orcid.org/0000-0002-5108-6823

Lindy Blackburn https://orcid.org/0000-0002-9030-642X

Raymond Blundell https://orcid.org/0000-0002-5929-5857

Katherine L. Bouman https://orcid.org/0000-0003-0077-4367

Geoffrey C. Bower https://orcid.org/0000-0003-4056-9982

Hope Boyce https://orcid.org/0000-0002-6530-5783

Christiaan D. Brinkerink https://orcid.org/0000-0002-2322-0749

Roger Brissenden https://orcid.org/0000-0002-2556-0894

Silke Britzen https://orcid.org/0000-0001-9240-6734

Avery E. Broderick https://orcid.org/0000-0002-3351-760X

Do-Young Byun https://orcid.org/0000-0003-1157-4109

Andrew Chael https://orcid.org/0000-0003-2966-6220

Chi-kwan Chan https://orcid.org/0000-0001-6337-6126

Shami Chatterjee https://orcid.org/0000-0002-2878-1502

Koushik Chatterjee https://orcid.org/0000-0002-2825-3590

Paul M. Chesler https://orcid.org/0000-0001-6327-8462

Ilje Cho https://orcid.org/0000-0001-6083-7521

Pierre Christian https://orcid.org/0000-0001-6820-9941

John E. Conway https://orcid.org/0000-0003-2448-9181

James M. Cordes https://orcid.org/0000-0002-4049-1882

Thomas M. Crawford https://orcid.org/0000-0001-9000-5013

Geoffrey B. Crew https://orcid.org/0000-0002-2079-3189

Alejandro Cruz-Osorio https://orcid.org/0000-0002-3945-6342

Yuzhu Cui https://orcid.org/0000-0001-6311-4345

Jordy Davelaar https://orcid.org/0000-0002-2685-2434

Mariafelicia De Laurentis https://orcid.org/0000-0002-9945-682X

Roger Deane https://orcid.org/0000-0003-1027-5043

Jessica Dempsey https://orcid.org/0000-0003-1269-9667

Gregory Desvignes https://orcid.org/0000-0003-3922-4055

Jason Dexter https://orcid.org/0000-0003-3903-0373

Sheperd S. Doeleman https://orcid.org/0000-0002-9031-0904

Ralph P. Eatough https://orcid.org/0000-0001-6196-4135

Heino Falcke https://orcid.org/0000-0002-2526-6724

Joseph Farah https://orcid.org/0000-0003-4914-5625

Vincent L. Fish https://orcid.org/0000-0002-7128-9345

Ed Fomalont https://orcid.org/0000-0002-9036-2747

H. Alyson Ford https://orcid.org/0000-0002-9797-0972

Raquel Fraga-Encinas https://orcid.org/0000-0002-5222-1361

Per Friberg https://orcid.org/0000-0002-8010-8454

Antonio Fuentes https://orcid.org/0000-0002-8773-4933

Peter Galison https://orcid.org/0000-0002-6429-3872

Charles F. Gammie https://orcid.org/0000-0001-7451-8935

Roberto García https://orcid.org/0000-0002-6584-7443

Boris Georgiev https://orcid.org/0000-0002-3586-6424

Ciriaco Goddi https://orcid.org/0000-0002-2542-7743

Roman Gold https://orcid.org/0000-0003-2492-1966

José L. Gómez https://orcid.org/0000-0003-4190-7613

Arturo I. Gómez-Ruiz https://orcid.org/0000-0001-9395-1670

Minfeng Gu (顾敏峰) https://orcid.org/0000-0002-4455-6946

Mark Gurwell https://orcid.org/0000-0003-0685-3621

Kazuhiro Hada https://orcid.org/0000-0001-6906-772X

Daryl Haggard https://orcid.org/0000-0001-6803-2138

Ronald Hesper https://orcid.org/0000-0003-1918-6098

Luis C. Ho (何子山) https://orcid.org/0000-0001-6947-5846

Mareki Honma https://orcid.org/0000-0003-4058-9000

Chih-Wei L. Huang https://orcid.org/0000-0001-5641-3953
Shiro Ikeda https://orcid.org/0000-0002-2462-1448

Sara Issaoun https://orcid.org/0000-0002-5297-921X

David J. James https://orcid.org/0000-0001-5160-4486

Michael Janssen https://orcid.org/0000-0001-6865-6544

Britton Jeter https://orcid.org/0000-0003-2847-1712

Wu Jiang (江悟) https://orcid.org/0000-0001-7369-3539

Michael D. Johnson https://orcid.org/0000-0002-4120-3029

Svetlana Jorstad https://orcid.org/0000-0001-6158-1708

Taehyun Jung https://orcid.org/0000-0001-7003-8643

Mansour Karami https://orcid.org/0000-0001-7387-9333

Ramesh Karuppusamy https://orcid.org/0000-0002-5307-2919

Tomohisa Kawashima https://orcid.org/0000-0001-8527-0496

Garrett K. Keating https://orcid.org/0000-0002-3490-146X

Mark Kettenis https://orcid.org/0000-0002-6156-5617

Dong-Jin Kim https://orcid.org/0000-0002-7038-2118

Jae-Young Kim https://orcid.org/0000-0001-8229-7183

Jongsoo Kim https://orcid.org/0000-0002-1229-0426

Junhan Kim https://orcid.org/0000-0002-4274-9373

Motoki Kino https://orcid.org/0000-0002-2709-7338

Jun Yi Koay https://orcid.org/0000-0002-7029-6658

Patrick M. Koch https://orcid.org/0000-0003-2777-5861

Shoko Koyama https://orcid.org/0000-0002-3723-3372

Michael Kramer https://orcid.org/0000-0002-4175-2271

Carsten Kramer https://orcid.org/0000-0002-4908-4925

Thomas P. Krichbaum https://orcid.org/0000-0002-4892-9586

Cheng-Yu Kuo https://orcid.org/0000-0001-6211-5581

Tod R. Lauer https://orcid.org/0000-0003-3234-7247

Sang-Sung Lee https://orcid.org/0000-0002-6269-594X

Aviad Levis https://orcid.org/0000-0001-7307-632X

Yan-Rong Li (李彦荣) https://orcid.org/0000-0001-5841-9179

Zhiyuan Li (李志远) https://orcid.org/0000-0003-0355-6437

Michael Lindqvist https://orcid.org/0000-0002-3669-0715

Rocco Lico https://orcid.org/0000-0001-7361-2460

Greg Lindahl https://orcid.org/0000-0002-6100-4772

Jun Liu (刘俊) https://orcid.org/0000-0002-7615-7499

Kuo Liu https://orcid.org/0000-0002-2953-7376

Elisabetta Liuzzo https://orcid.org/0000-0003-0995-5201

Laurent Loinard https://orcid.org/0000-0002-5635-3345

Ru-Sen Lu (路如森) https://orcid.org/0000-0002-7692-7967

Nicholas R. MacDonald https://orcid.org/0000-0002-6684-8691

Jirong Mao (毛基荣) https://orcid.org/0000-0002-7077-7195

Nicola Marchili https://orcid.org/0000-0002-5523-7588

Sera Markoff https://orcid.org/0000-0001-9564-0876

Daniel P. Marrone https://orcid.org/0000-0002-2367-1080

Alan P. Marscher https://orcid.org/0000-0001-7396-3332

Iván Martí-Vidal https://orcid.org/0000-0003-3708-9611

Satoki Matsushita https://orcid.org/0000-0002-2127-7880

Lynn D. Matthews https://orcid.org/0000-0002-3728-8082

Lia Medeiros https://orcid.org/0000-0003-2342-6728

Karl M. Menten https://orcid.org/0000-0001-6459-0669

Izumi Mizuno https://orcid.org/0000-0002-7210-6264

Yosuke Mizuno https://orcid.org/0000-0002-8131-6730

James M. Moran https://orcid.org/0000-0002-3882-4414

Kotaro Moriyama https://orcid.org/0000-0003-1364-3761

Monika Moscibrodzka https://orcid.org/0000-0002-4661-6332

Cornelia Müller https://orcid.org/0000-0002-2739-2994

Gibwa Musoke https://orcid.org/0000-0003-1984-189X

Alejandro Mus Mejías https://orcid.org/0000-0003-0329-6874

Daniel Michalik https://orcid.org/0000-0002-7618-6556

Andrew Nadolski https://orcid.org/0000-0001-9479-9957

Hiroshi Nagai https://orcid.org/0000-0003-0292-3645

Neil M. Nagar https://orcid.org/0000-0001-6920-662X

Masanori Nakamura https://orcid.org/0000-0001-6081-2420

Ramesh Narayan https://orcid.org/0000-0002-1919-2730

Iniyan Natarajan https://orcid.org/0000-0001-8242-4373

Joey Neilsen https://orcid.org/0000-0002-8247-786X

Roberto Neri https://orcid.org/0000-0002-7176-4046

Chunchong Ni https://orcid.org/0000-0003-1361-5699

Aristeidis Noutsos https://orcid.org/0000-0002-4151-3860

Michael A. Nowak https://orcid.org/0000-0001-6923-1315

Héctor Olivares https://orcid.org/0000-0001-6833-7580

Gisela N. Ortiz-León https://orcid.org/0000-0002-2863-676X

Daniel C. M. Palumbo https://orcid.org/0000-0002-7179-3816

Jongho Park https://orcid.org/0000-0001-6558-9053

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Dominic W. Pesce https://orcid.org/0000-0002-5278-9221

Richard Plambeck https://orcid.org/0000-0001-6765-9609

Oliver Porth https://orcid.org/0000-0002-4584-2557

Felix M. Pötzl https://orcid.org/0000-0002-6579-8311

Ben Prather https://orcid.org/0000-0002-0393-7734

Jorge A. Preciado-López https://orcid.org/0000-0002-4146-0113

Hung-Yi Pu https://orcid.org/0000-0001-9270-8812

Venkatessh Ramakrishnan https://orcid.org/0000-0002-9248-086X

Ramprasad Rao https://orcid.org/0000-0002-1407-7944

Mark G. Rawlings https://orcid.org/0000-0002-6529-202X

Alexander W. Raymond https://orcid.org/0000-0002-5779-4767

Luciano Rezzolla https://orcid.org/0000-0002-1330-7103

Angelo Ricarte https://orcid.org/0000-0001-5287-0452

Bart Ripperda https://orcid.org/0000-0002-7301-3908

Freek Roelofs https://orcid.org/0000-0001-5461-3687

Eduardo Ros https://orcid.org/0000-0001-9503-4892

Mel Rose https://orcid.org/0000-0002-2016-8746

Alan L. Roy https://orcid.org/0000-0002-1931-0135

Chet Ruszczyk https://orcid.org/0000-0001-7278-9707

Kazi L. J. Rygl https://orcid.org/0000-0003-4146-9043

David Sánchez-Arguelles https://orcid.org/0000-0002-7344-9920

Mahito Sasada https://orcid.org/0000-0001-5946-9960

Tuomas Savolainen https://orcid.org/0000-0001-6214-1085

Karl-Friedrich Schuster https://orcid.org/0000-0003-2890-9454

Lijing Shao https://orcid.org/0000-0002-1334-8853

Zhiqiang Shen (沈志强) https://orcid.org/0000-0003-3540-8746

Des Small https://orcid.org/0000-0003-3723-5404

Bong Won Sohn https://orcid.org/0000-0002-4148-8378

Jason SooHoo https://orcid.org/0000-0003-1938-0720

He Sun (孙赫) https://orcid.org/0000-0003-1526-6787
Fumie Tazaki https://orcid.org/0000-0003-0236-0600

Alexandra J. Tetarenko https://orcid.org/0000-0003-3906-4354

Paul Tiede https://orcid.org/0000-0003-3826-5648

Remo P. J. Tilanus https://orcid.org/0000-0002-6514-553X

Michael Titus https://orcid.org/0000-0002-3423-4505

Kenji Toma https://orcid.org/0000-0002-7114-6010

Pablo Torne https://orcid.org/0000-0001-8700-6058

Efthalia Traianou https://orcid.org/0000-0002-1209-6500

Sascha Trippe https://orcid.org/0000-0003-0465-1559

Ilse van Bemmel https://orcid.org/0000-0001-5473-2950

Huib Jan van Langevelde https://orcid.org/0000-0002-0230-5946

Daniel R. van Rossum https://orcid.org/0000-0001-7772-6131

Jan Wagner https://orcid.org/0000-0003-1105-6109

Derek Ward-Thompson https://orcid.org/0000-0003-1140-2761

John Wardle https://orcid.org/0000-0002-8960-2942

Jonathan Weintroub https://orcid.org/0000-0002-4603-5204

Norbert Wex https://orcid.org/0000-0003-4058-2837

Robert Wharton https://orcid.org/0000-0002-7416-5209

Maciek Wielgus https://orcid.org/0000-0002-8635-4242

George N. Wong https://orcid.org/0000-0001-6952-2147

Qingwen Wu (吴庆文) https://orcid.org/0000-0003-4773-4987

Doosoo Yoon https://orcid.org/0000-0001-8694-8166

André Young https://orcid.org/0000-0003-0000-2682

Ken Young https://orcid.org/0000-0002-3666-4920

Ziri Younsi https://orcid.org/0000-0001-9283-1191

Feng Yuan (袁峰) https://orcid.org/0000-0003-3564-6437

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Guang-Yao Zhao https://orcid.org/0000-0002-4417-1659

Shan-Shan Zhao https://orcid.org/0000-0002-9774-3606

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Kazunori Akiyama¹,²,³ D, Juan Carlos Algaba⁴ D, Antxon Alberdi⁵ D, Walter Alef⁶, Richard Anantua³,⁷,⁸ D, Keiichi Asada⁹, Rebecca Azulay⁶,¹⁰,¹¹ D, Anne-Kathrin Baczko⁶ D, David Ball¹², Mislav Baloković¹³,¹⁴ D, John Barrett¹ D, Bradford A. Benson¹⁵,¹⁶ D, Dan Bintley¹⁷, Lindy Blackburn³,⁷ D, Raymond Blundell⁷ D, Wilfred Boland¹⁸, Katherine L. Bouman³,⁷,¹⁹ D, Geoffrey C. Bower²⁰ D, Hope Boyce²¹,²² D, Michael Bremer²³, Christiaan D. Brinkerink²⁴ D, Roger Brissenden³,⁷ D, Silke Britzen⁶ D, Avery E. Broderick²⁵,²⁶,²⁷ D, Dominique Broguiere²³, Thomas Bronzwaer²⁴, Do-Young Byun²⁸,²⁹ D, John E. Carlstrom¹⁶,³⁰,³¹,³², Andrew Chael³³,¹²⁷ D, Chi-kwan Chan¹²,³⁴ D, Shami Chatterjee³⁵ D, Koushik Chatterjee³⁶ D, Ming-Tang Chen²⁰, Yongjun Chen (陈永军)³⁷,³⁸, Paul M. Chesler³ D, Ilje Cho²⁸,²⁹ D, Pierre Christian³⁹ D, John E. Conway⁴⁰ D, James M. Cordes³⁵ D, Thomas M. Crawford¹⁶,³⁰ D, Geoffrey B. Crew¹ D, Alejandro Cruz-Osorio⁴¹ D, Yuzhu Cui⁴²,⁴³ D, Jordy Davelaar⁸,²⁴,⁴⁴ D, Mariafelia De Laurentis⁴¹,⁴⁵,⁴⁶ D, Roger Deane⁴⁷,⁴⁸,⁴⁹ D, Jessica Dempsey¹⁷ D, Gregory Desvignes⁵⁰ D, Jason Dexter⁵¹ D, Sheperd S. Doeleman³,⁷ D, Ralph P. Eatough⁶,⁵² D, Heino Falcke²⁴ D, Joseph Farah³,⁷,⁵³ D, Vincent L. Fish¹ D, Ed Fomalont⁵⁴ D, H. Alyson Ford¹² D, Raquel Fraga-Encinas²⁴ D, William T. Freeman⁵⁵,⁵⁶ D, Per Friberg¹⁷ D, Christian M. Fromm³,⁷,⁴¹, Antonio Fuentes⁵ D, Peter Galison³,⁵⁷,⁵⁸ D, Charles F. Gammie⁵⁹,⁶⁰ D, Roberto García²³ D, Olivier Gentaz²³, Boris Georgiev²⁶,²⁷ D, Ciriaco Goddi²⁴,⁶¹ D, Roman Gold²⁵,⁶² D, José L. Gómez⁵ D, Arturo I. Gómez-Ruiz⁶³,⁶⁴ D, Minfeng Gu (顾敏峰)³⁷,⁶⁵ D, Mark Gurwell⁷ D, Kazuhiro Hada⁴²,⁴³ D, Daryl Haggard²¹,²² D, Michael H. Hecht¹, Ronald Hesper⁶⁶ D, Luis C. Ho (何子山)⁶⁷,⁶⁸ D, Paul Ho⁹, Mareki Honma⁴²,⁴³,⁶⁹ D, Chih-Wei L. Huang⁹ D, Lei Huang (黄磊)³⁷,⁶⁵, David H. Hughes⁶³, Shiro Ikeda²,⁷⁰,⁷¹,⁷² D, Makoto Inoue⁹, Sara Issaoun²⁴ D, David J. James⁷³ D, Buell T. Jannuzi¹², Michael Janssen⁶ D, Britton Jeter²⁶,²⁷ D, Wu Jiang (江悟)³⁷ D, Alejandra Jimenez-Rosales²⁴, Michael D. Johnson³,⁷ D, Svetlana Jorstad⁷⁴,⁷⁵ D, Taehyun Jung²⁸,²⁹ D, Mansour Karami²⁵,²⁶ D, Ramesh Karuppusamy⁶ D, Tomohisa Kawashima⁷⁶ D, Garrett K. Keating⁷ D, Mark Kettenis⁷⁷ D, Dong-Jin Kim⁶ D, Jae-Young Kim⁶,²⁸ D, Jongsoo Kim²⁸ D, Junhan Kim¹²,¹⁹ D, Motoki Kino²,⁷⁸ D, Jun Yi Koay⁹ D, Yutaro Kofuji⁴²,⁶⁹, Patrick M. Koch⁹ D, Shoko Koyama⁹ D, Michael Kramer⁶ D, Carsten Kramer²³ D, Thomas P. Krichbaum⁶ D, Cheng-Yu Kuo⁷⁹,⁹ D, Tod R. Lauer⁸⁰ D, Sang-Sung Lee²⁸ D, Aviad Levis¹⁹ D, Yan-Rong Li (李彦荣)⁸¹ D, Zhiyuan Li (李志远)⁸²,⁸³ D, Michael Lindqvist⁴⁰ D, Rocco Lico⁵,⁶ D, Greg Lindahl⁷ D, Jun Liu (刘俊)⁶ D, Kuo Liu⁶ D, Elisabetta Liuzzo⁸⁴ D, Wen-Ping Lo⁹,⁸⁵, Andrei P. Lobanov⁶, Laurent Loinard⁸⁶,⁸⁷ D, Colin Lonsdale¹, Ru-Sen Lu (路如森)³⁷,³⁸,⁶ D, Nicholas R. MacDonald⁶ D, Jirong Mao (毛基荣)⁸⁸,⁸⁹,⁹⁰ D, Nicola Marchili⁶,⁸⁴ D, Sera Markoff³⁶,⁹¹ D, Daniel P. Marrone¹² D, Alan P. Marscher⁷⁴ D, Iván Martí-Vidal¹⁰,¹¹ D, Satoki Matsushita⁹ D, Lynn D. Matthews¹ D, Lia Medeiros¹²,⁹² D, Karl M. Menten⁶ D, Izumi Mizuno¹⁷ D, Yosuke Mizuno⁴¹,⁹³ D, James M. Moran³,⁷ D, Kotaro Moriyama¹,⁴² D, Monika Moscibrodzka²⁴ D, Cornelia Müller⁶,²⁴ D, Gibwa Musoke²⁴,³⁶ D, Alejandro Mus Mejías¹⁰,¹¹ D, Daniel Michalik⁹⁴,⁹⁵ D, Andrew Nadolski⁶⁰ D, Hiroshi Nagai²,⁴³ D, Neil M. Nagar⁹⁶ D, Masanori Nakamura⁹,⁹⁷ D, Ramesh Narayan³,⁷ D, Gopal Narayanan⁹⁸, Iniyan Natarajan⁴⁷,⁴⁹,⁹⁹ D, Antonios Nathanail⁴¹,¹⁰⁰, Joey Neilsen¹⁰¹ D, Roberto Neri²³ D, Chunchong Ni²⁶,²⁷ D, Aristeidis Noutsos⁶ D, Michael A. Nowak¹⁰² D, Hiroki Okino⁴²,⁶⁹, Héctor Olivares²⁴ D, Gisela N. Ortiz-León⁶ D, Tomoaki Oyama⁴², Feryal Özel¹², Daniel C. M. Palumbo³,⁷ D, Jongho Park⁹,¹²⁸ D, Nimesh Patel⁷, Ue-Li Pen²⁵,¹⁰³,¹⁰⁴,¹⁰⁵ D, Dominic W. Pesce³,⁷ D, Vincent Piétu²³, Richard Plambeck¹⁰⁶ D, Aleksandar PopStefanija⁹⁸, Oliver Porth³⁶,⁴¹ D, Felix M. Pötzl⁶ D, Ben Prather⁵⁸ D, Jorge A. Preciado-López²⁵ D, Dimitrios Psaltis¹², Hung-Yi Pu⁹,²⁵,¹⁰⁷ D, Venkatessh Ramakrishnan⁹⁶ D, Ramprasad Rao²⁰ D, Mark G. Rawlings¹⁷ D, Alexander W. Raymond³,⁷ D, Luciano Rezzolla⁴¹,¹⁰⁸,¹⁰⁹ D, Angelo Ricarte³,⁷ D, Bart Ripperda⁸,¹¹⁰ D, Freek Roelofs²⁴ D, Alan Rogers¹, Eduardo Ros⁶ D, Mel Rose¹² D, Arash Roshanineshat¹², Helge Rottmann⁶, Alan L. Roy⁶ D, Chet Ruszczyk¹ D, Kazi L. J. Rygl⁸⁴ D, Salvador Sánchez¹¹¹, David Sánchez-Arguelles⁶³,⁶⁴ D, Mahito Sasada⁴²,¹¹² D, Tuomas Savolainen⁶,¹¹³,¹¹⁴ D, F. Peter Schloerb⁹⁸, Karl-Friedrich Schuster²³ D, Lijing Shao⁶,⁶⁸ D, Zhiqiang Shen (沈志强)³⁷,³⁸ D, Des Small⁷⁷ D, Bong Won Sohn²⁸,²⁹,¹¹⁵ D, Jason SooHoo¹ D, He Sun (孙赫)¹⁹ D, Fumie Tazaki⁴² D, Alexandra J. Tetarenko¹⁷ D, Paul Tiede²⁶,²⁷ D, Remo P. J. Tilanus¹²,²⁴,⁶¹,¹¹⁶ D, Michael Titus¹ D, Kenji Toma¹¹⁷,¹¹⁸ D, Pablo Torne⁶,¹¹¹ D, Tyler Trent¹², Efthalia Traianou⁶ D, Sascha Trippe¹¹⁹ D, Ilse van Bemmel⁷⁷ D, Huib Jan van Langevelde⁷⁷,¹²⁰ D, Daniel R. van Rossum²⁴ D, Jan Wagner⁶ D, Derek Ward-Thompson¹²¹ D, John Wardle¹²² D, Jonathan Weintroub³,⁷ D, Norbert Wex⁶ D, Robert Wharton⁶ D, Maciek Wielgus³,⁷ D, George N. Wong⁵⁹ D, Qingwen Wu (吴庆文)¹²³ D, Doosoo Yoon³⁶ D, André Young²⁴ D, Ken Young⁷ D,
Ziri Younsi<sup>41,124,129</sup> ID, Feng Yuan (袁峰)<sup>37,65,125</sup> ID, Ye-Fei Yuan (袁业飞)<sup>126</sup> ID, J. Anton Zensus<sup>6</sup> ID, Guang-Yao Zhao<sup>5</sup> ID, and Shan-Shan Zhao<sup>37</sup> ID

The Event Horizon Telescope Collaboration

¹ Massachusetts Institute of Technology Haystack Observatory, 99 Millstone Road, Westford, MA 01886, USA

² National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

³ Black Hole Initiative at Harvard University, 20 Garden Street, Cambridge, MA 02138, USA

⁴ Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia

⁵ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain

⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA

⁸ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA

⁹ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No. 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C.

¹⁰ Departament d'Astronomia i Astrofísica, Universitat de València, C. Dr. Moliner 50, E-46100 Burjassot, València, Spain

¹¹ Observatori Astronòmic, Universitat de València, C. Catedrático José Beltrán 2, E-46980 Paterna, València, Spain

¹² Steward Observatory and Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

¹³ Yale Center for Astronomy & Astrophysics, 52 Hillhouse Avenue, New Haven, CT 06511, USA

¹⁴ Department of Physics, Yale University, P.O. Box 2018120, New Haven, CT 06520, USA

¹⁵ Fermi National Accelerator Laboratory, MS209, P.O. Box 500, Batavia, IL, 60510, USA

¹⁶ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

¹⁷ East Asian Observatory, 660 North A'ohoku Place, Hilo, HI 96720, USA

¹⁸ Nederlandse Onderzoekschool voor Astronomie (NOVA), PO Box 9513, 2300 RA Leiden, The Netherlands

¹⁹ California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA

²⁰ Institute of Astronomy and Astrophysics, Academia Sinica, 645 North A'ohoku Place, Hilo, HI 96720, USA

²¹ Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada

²² McGill Space Institute, McGill University, 3550 rue University, Montréal, QC H3A 2A7, Canada

²³ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France

²⁴ Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands

²⁵ Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON, N2L 2Y5, Canada

²⁶ Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada

²⁷ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

²⁸ Korea Astronomy and Space Science Institute, Daedeo-daero 776, Yuseong-gu, Daejeon 34055, Republic of Korea

²⁹ University of Science and Technology, Gajeong-ro 217, Yuseong-gu, Daejeon 34013, Republic of Korea

³⁰ Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

³¹ Department of Physics, University of Chicago, 5720 South Ellis Avenue, Chicago, IL 60637, USA

³² Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

³³ Princeton Center for Theoretical Science, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA

³⁴ Data Science Institute, University of Arizona, 1230 North Cherry Avenue, Tucson, AZ 85721, USA

³⁵ Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853, USA

³⁶ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands

³⁷ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People's Republic of China

³⁸ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, People's Republic of China

³⁹ Physics Department, Fairfield University, 1073 North Benson Road, Fairfield, CT 06824, USA

⁴⁰ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden

⁴¹ Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany

⁴² Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa, Oshu, Iwate 023-0861, Japan

⁴³ Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

⁴⁴ Department of Astronomy and Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA

⁴⁵ Dipartimento di Fisica “E. Pancini”, “Università di Napoli “Federico II,” Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126, Napoli, Italy

⁴⁶ INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126, Napoli, Italy

⁴⁷ Wits Centre for Astrophysics, University of Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa

⁴⁸ Department of Physics, University of Pretoria, Hatfield, Pretoria 0028, South Africa

⁴⁹ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Makhanda 6140, South Africa

⁵⁰ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France

⁵¹ JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA

⁵² National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, People's Republic of China

⁵³ University of Massachusetts Boston, 100 William T. Morrissey Boulevard, Boston, MA 02125, USA

⁵⁴ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

⁵⁵ Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 32-D476, 77 Massachusetts Avenue, Cambridge, MA 02142, USA

⁵⁶ Google Research, 355 Main Street, Cambridge, MA 02142, USA

⁵⁷ Department of History of Science, Harvard University, Cambridge, MA 02138, USA

⁵⁸ Department of Physics, Harvard University, Cambridge, MA 02138, USA

⁵⁹ Department of Physics, University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA

⁶⁰ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA

⁶¹ Leiden Observatory—Allegro, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

⁶² CP3-Origins, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark

⁶³ Instituto Nacional de Astrofísica, Óptica y Electrónica. Apartado Postal 51 y 216, 72000. Puebla Pue., México

⁶⁴ Consejo Nacional de Ciencia y Tecnología, Av. Insurgentes Sur 1582, 03940, Ciudad de México, México

⁶⁵ Key Laboratory for Research in Galaxies and Cosmology, Chinese Academy of Sciences, Shanghai 200030, People's Republic of China

⁶⁶ NOVA Sub-mm Instrumentation Group, Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands

⁶⁷ Department of Astronomy, School of Physics, Peking University, Beijing 100871, People's Republic of China

⁶⁸ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China
⁶⁹ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

⁷⁰ The Institute of Statistical Mathematics, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8562, Japan

⁷¹ Department of Statistical Science, The Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan

⁷² Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8583, Japan

⁷³ ASTRAVEO, LLC, PO Box 1668, Gloucester, MA 01931, USA

⁷⁴ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

⁷⁵ Astronomical Institute, St. Petersburg University, Universitetskij pr., 28, Petrodvorets, 198504 St. Petersburg, Russia

⁷⁶ Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan

⁷⁷ Joint Institute for VLBI ERIC (JIVE), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

⁷⁸ Kogakuin University of Technology & Engineering, Academic Support Center, 2665-1 Nakano, Hachioji, Tokyo 192-0015, Japan

⁷⁹ Physics Department, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaosiung City 80424, Taiwan, R.O.C.

⁸⁰ National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA

⁸¹ Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Shijingshan District, Beijing, People's Republic of China

⁸² School of Astronomy and Space Science, Nanjing University, Nanjing 210023, People's Republic of China

⁸³ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210023, People's Republic of China

⁸⁴ Italian ALMA Regional Centre, INAF-Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna, Italy

⁸⁵ Department of Physics, National Taiwan University, No. 1, Sect. 4, Roosevelt Road, Taipei 10617, Taiwan, R.O.C.

⁸⁶ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58089, México

⁸⁷ Instituto de Astronomía, Universidad Nacional Autónoma de México, CdMx 04510, México

⁸⁸ Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, Yunnan Province, People's Republic of China

⁸⁹ Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing, 100012, People's Republic of China

⁹⁰ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, People's Republic of China

⁹¹ Gravitation Astroparticle Physics Amsterdam (GRAPPA) Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

⁹² School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA

⁹³ Tsung-Dao Lee Institute and School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, People's Republic of China

⁹⁴ Science Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

⁹⁵ University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

⁹⁶ Astronomy Department, Universidad de Concepción, Casilla 160-C, Concepción, Chile

⁹⁷ National Institute of Technology, Hachinohe College, 16-1 Uwanotai, Tamonoki, Hachinohe City, Aomori 039-1192, Japan

⁹⁸ Department of Astronomy, University of Massachusetts, 01003, Amherst, MA, USA

⁹⁹ South African Radio Astronomy Observatory, Observatory 7925, Cape Town, South Africa

¹⁰⁰ Department of Physics, National and Kapodistrian University of Athens, Panepistimiopolis, GR 15783 Zografos, Greece

¹⁰¹ Villanova University, Mendel Science Center Rm. 263B, 800 East Lancaster Avenue, Villanova PA 19085, USA

¹⁰² Physics Department, Washington University CB 1105, St Louis, MO 63130, USA

¹⁰³ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada

¹⁰⁴ Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada

¹⁰⁵ Canadian Institute for Advanced Research, 180 Dundas Street West, Toronto, ON M5G 1Z8, Canada

¹⁰⁶ Radio Astronomy Laboratory, University of California, Berkeley, CA 94720, USA

¹⁰⁷ Department of Physics, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Rd., Taipei 116, Taiwan, R.O.C.

¹⁰⁸ Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, 60438 Frankfurt, Germany

¹⁰⁹ School of Mathematics, Trinity College, Dublin 2, Ireland

¹¹⁰ Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA

¹¹¹ Instituto de Radioastronomía Milimétrica, IRAM, Avenida Divina Pastora 7, Local 20, E-18012, Granada, Spain

¹¹² Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan

¹¹³ Aalto University Department of Electronics and Nanoengineering, PL 15500, FI-00076 Aalto, Finland

¹¹⁴ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, Finland

¹¹⁵ Department of Astronomy, Yonsei University, Yonsei-ro 50, Seodaemun-gu, 03722 Seoul, Republic of Korea

¹¹⁶ Netherlands Organisation for Scientific Research (NWO), Postbus 93138, 2509 AC Den Haag, The Netherlands

¹¹⁷ Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan

¹¹⁸ Astronomical Institute, Tohoku University, Sendai 980-8578, Japan

¹¹⁹ Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea

¹²⁰ Leiden Observatory, Leiden University, Postbus 2300, 9513 RA Leiden, The Netherlands

¹²¹ Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK

¹²² Physics Department, Brandeis University, 415 South Street, Waltham, MA 02453, USA

¹²³ School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, People's Republic of China

¹²⁴ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK

¹²⁵ School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, People's Republic of China

¹²⁶ Astronomy Department, University of Science and Technology of China, Hefei 230026, People's Republic of China