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First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration

Kazunori Akiyama Antxon Alberdi Walter Alef Juan Carlos Algaba Richard Anantua Keiichi Asada Rebecca Azulay Uwe Bach Anne-Kathrin Baczko David Ball Mislav Baloković John Barrett Michi Bauböck Bradford A. Benson Dan Bintley Lindy Blackburn Raymond Blundell Katherine L. Bouman Geoffrey C. Bower Hope Boyce Michael Bremer Christiaan D. Brinkerink Roger Brissenden Silke Britzen Avery E. Broderick Dominique Broguiere Thomas Bronzwaer Sandra Bustamante Do-Young Byun John E. Carlstrom Chiara Ceccobello Andrew Chael Chi-Kwan Chan Koushik Chatterjee Shami Chatterjee Ming-Tang Chen Yongjun Chen Xiaopeng Cheng Ilje Cho Pierre Christian Nicholas S. Conroy John E. Conway James M. Cordes Thomas M. Crawford Geoffrey B. Crew Alejandro Cruz-Osorio Yuzhu Cui Jordy Davelaar Mariafelicia de Laurentis Roger Deane Jessica Dempsey Gregory Desvignes 1 Jason Dexter Vedant Dhruv Sheperd S. Doeleman Sean Dougal Sergio A. Dzib Ralph P. Eatough Razieh Emami Heino Falcke Joseph Farah Vincent L. Fish Ed Fomalont H. Alyson Ford Raquel Fraga-Encinas William T. Freeman Per Friberg Christian M. Fromm Antonio Fuentes Peter Galison Charles F. Gammie Roberto García Olivier Gentaz Boris Georgiev Ciriaco Goddi Roman Gold Arturo I. Gómez-Ruiz José L. Gómez Minfeng Gu Mark Gurwell Kazuhiro Hada Daryl Haggard Kari Haworth Michael H. Hecht Ronald Hesper Dirk Heumann Luis C. Ho Paul Ho Mareki Honma Chih-Wei L. Huang Lei Huang David H. Hughes Shiro Ikeda C. M. Violette Impellizzeri Makoto Inoue Sara Issaoun David J. James Buell T. Jannuzi Michael Janssen Britton Jeter Wu Jiang Alejandra Jiménez-Rosales Michael D. Johnson Svetlana Jorstad Abhishek V. Joshi Taehyun Jung Mansour Karami Ramesh Karuppusamy Tomohisa Kawashima Garrett K. Keating Mark Kettenis Dong-Jin Kim Jae-Young Kim Jongsoo Kim Junhan Kim Motoki Kino Jun Yi Koay Prashant Kocherlakota Yutaro Kofuji Patrick M. Koch Shoko Koyama Carsten Kramer Michael Kramer Thomas P. Krichbaum Cheng-Yu Kuo Noemi La Bella Tod R. Lauer Daeyoung Lee Sang-Sung Lee Po Kin Leung Aviad Levis Zhiyuan Li Rocco Lico Greg Lindahl Michael Lindqvist Mikhail Lisakov Jun Liu Kuo Liu Elisabetta Liuzzo Wen-Ping Lo Andrei P. Lobanov Laurent Loinard Colin J. Lonsdale Ru-Sen Lu Jirong Mao Nicola Marchili Sera Markoff Daniel P. Marrone Alan P. Marscher Iván Martí-Vidal Satoki Matsushita Lynn D. Matthews Lia Medeiros Karl M. Menten Daniel Michalik Izumi Mizuno Yosuke Mizuno James M. Moran Kotaro Moriyama Monika Moscibrodzka Cornelia Müller Alejandro Mus Gibwa Musoke Ioannis Myserlis Andrew Nadolski Hiroshi Nagai Neil M. Nagar Masanori Nakamura Ramesh Narayan Gopal Narayanan Iniyan Natarajan Antonios Nathanail Santiago Navarro Fuentes Joey Neilsen Roberto Neri Chunchong Ni Aristeidis Noutsos Michael A. Nowak Junghwan Oh Hiroki Okino Héctor Olivares Gisela N. Ortiz-León Tomoaki Oyama Feryal Özel Daniel C. M. Palumbo Georgios Filippos Paraschos Jongho Park Harriet Parsons Nimesh Patel Ue-Li Pen Dominic W. Pesce Vincent Piétu Richard Plambeck Aleksandar Popstefanija Oliver Porth Felix M. Pötzl Ben Prather Jorge A. Preciado-López Dimitrios Psaltis Hung-Yi Pu Venkatessh Ramakrishnan Ramprasad Rao Mark G. Rawlings Alexander W. Raymond Luciano Rezzolla Angelo Ricarte Bart Ripperda Freek Roelofs Alan Rogers Eduardo Ros Cristina Romero-Cañizales Arash Roshanineshat Helge Rottmann Alan L. Roy Ignacio Ruiz Chet Ruszczyk Kazi L. J. Rygl Salvador Sánchez David Sánchez-Argüelles Miguel Sánchez-Portal Mahito Sasada Kaushik Satapathy Tuomas Savolainen F. Peter Schloerb Jonathan Schonfeld Karl-Friedrich Schuster Lijing Shao Zhiqiang Shen Des Small Bong Won Sohn Jason Soohoo Kamal Souccar He Sun Fumie Tazaki Alexandra J. Tetarenko Paul Tiede Remo P. J. Tilanus Michael Titus Pablo Torne Efthalia Traianou Tyler Trent Sascha Trippe Matthew Turk Ilse van Bemmel Huib Jan van Langevelde Daniel R. van Rossum Jesse Vos Jan Wagner Derek Ward-Thompson John Wardle Jonathan Weintroub Norbert Wex Robert Wharton Maciek Wielgus Kaj Wiik Gunther Witzel Michael F. Wondrak George N. Wong Qingwen Wu Paul Yamaguchi Doosoo Yoon André Young Ken Young Ziri Younsi Feng Yuan Ye-Fei Yuan J. Anton Zensus Shuo Zhang Guang-Yao Zhao Shan-Shan Zhao Claudio Agurto Juan Pablo Araneda Oriel Arriagada Alessandra Bertarini Ryan Berthold Jay Blanchard Ken Brown Mauricio Cárdenas Michael Cantzler Patricio Caro Tim C. Chuter Miroslaw Ciechanowicz Iain M. Coulson Joseph Crowley Nathalie Degenaar Sven Dornbusch Carlos A. Durán Karl Forster Gertie Geertsema Edouard González Dave Graham Frédéric Gueth Chih-Chiang Han Cristian Herrera Ruben Herrero-Illana Stefan Heyminck James Hoge Yau-De Huang Homin Jiang David John Thomas Klein Derek Kubo John Kuroda Caleb Kwon Robert Laing Ching-Tang Liu Kuan-Yu Liu Felipe Mac-Auliffe Pierre Martin-Cocher Callie Matulonis Hugo Messias Zheng Meyer-Zhao Francisco Montenegro-Montes William Montgomerie Dirk Muders Hiroaki Nishioka Timothy J. Norton Rodrigo Olivares Juan Pablo Pérez-Beaupuits Rodrigo Parra Michael Poirier Nicolas Pradel Philippe A. Raffin Jorge Ramírez Mark Reynolds Alejandro F. Saez-Madain Jorge Santana Kevin M. Silva Don Sousa William Stahm Karl Torstensson Paulina Venegas Craig Walther Gundolf Wieching Rudy Wijnands Jan G. A. Wouterloot 
Abstract : We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5-11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ~50 μas, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.
Keywords : Black holes
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Submitted on : Monday, July 4, 2022 - 4:15:43 PM
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Kazunori Akiyama, Antxon Alberdi, Walter Alef, Juan Carlos Algaba, Richard Anantua, et al.. First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration. The Astrophysical Journal Letters, 2022, 930, ⟨10.3847/2041-8213/ac6675⟩. ⟨insu-03713316⟩

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