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

Author:

Event Horizon Telescope Collaboration ,Akiyama KazunoriORCID,Alberdi AntxonORCID,Alef Walter,Algaba Juan CarlosORCID,Anantua RichardORCID,Asada KeiichiORCID,Azulay RebeccaORCID,Bach UweORCID,Baczko Anne-KathrinORCID,Ball David,Baloković MislavORCID,Barrett JohnORCID,Bauböck MichiORCID,Benson Bradford A.ORCID,Bintley Dan,Blackburn LindyORCID,Blundell RaymondORCID,Bouman Katherine L.ORCID,Bower Geoffrey C.ORCID,Boyce HopeORCID,Bremer Michael,Brinkerink Christiaan D.ORCID,Brissenden RogerORCID,Britzen SilkeORCID,Broderick Avery E.ORCID,Broguiere DominiqueORCID,Bronzwaer ThomasORCID,Bustamante SandraORCID,Byun Do-YoungORCID,Carlstrom John E.ORCID,Ceccobello ChiaraORCID,Chael AndrewORCID,Chan Chi-kwanORCID,Chatterjee KoushikORCID,Chatterjee ShamiORCID,Chen Ming-TangORCID,Chen YongjunORCID,Cheng XiaopengORCID,Cho IljeORCID,Christian PierreORCID,Conroy Nicholas S.ORCID,Conway John E.ORCID,Cordes James M.ORCID,Crawford Thomas M.ORCID,Crew Geoffrey B.ORCID,Cruz-Osorio AlejandroORCID,Cui YuzhuORCID,Davelaar JordyORCID,De Laurentis MariafeliciaORCID,Deane RogerORCID,Dempsey JessicaORCID,Desvignes GregoryORCID,Dexter JasonORCID,Dhruv VedantORCID,Doeleman Sheperd S.ORCID,Dougal SeanORCID,Dzib Sergio A.ORCID,Eatough Ralph P.ORCID,Emami RaziehORCID,Falcke HeinoORCID,Farah JosephORCID,Fish Vincent L.ORCID,Fomalont EdORCID,Ford H. AlysonORCID,Fraga-Encinas RaquelORCID,Freeman William T.,Friberg PerORCID,Fromm Christian M.ORCID,Fuentes AntonioORCID,Galison PeterORCID,Gammie Charles F.ORCID,García RobertoORCID,Gentaz OlivierORCID,Georgiev BorisORCID,Goddi CiriacoORCID,Gold RomanORCID,Gómez-Ruiz Arturo I.ORCID,Gómez José L.ORCID,Gu MinfengORCID,Gurwell MarkORCID,Hada KazuhiroORCID,Haggard DarylORCID,Haworth Kari,Hecht Michael H.ORCID,Hesper RonaldORCID,Heumann DirkORCID,Ho Luis C.ORCID,Ho PaulORCID,Honma MarekiORCID,Huang Chih-Wei L.ORCID,Huang LeiORCID,Hughes David H.,Ikeda ShiroORCID,Impellizzeri C. M. VioletteORCID,Inoue MakotoORCID,Issaoun SaraORCID,James David J.ORCID,Jannuzi Buell T.ORCID,Janssen MichaelORCID,Jeter BrittonORCID,Jiang WuORCID,Jiménez-Rosales AlejandraORCID,Johnson Michael D.ORCID,Jorstad SvetlanaORCID,Joshi Abhishek V.ORCID,Jung TaehyunORCID,Karami MansourORCID,Karuppusamy RameshORCID,Kawashima TomohisaORCID,Keating Garrett K.ORCID,Kettenis MarkORCID,Kim Dong-JinORCID,Kim Jae-YoungORCID,Kim JongsooORCID,Kim JunhanORCID,Kino MotokiORCID,Koay Jun YiORCID,Kocherlakota PrashantORCID,Kofuji Yutaro,Koch Patrick M.ORCID,Koyama ShokoORCID,Kramer CarstenORCID,Kramer MichaelORCID,Krichbaum Thomas P.ORCID,Kuo Cheng-YuORCID,Bella Noemi LaORCID,Lauer Tod R.ORCID,Lee DaeyoungORCID,Lee Sang-SungORCID,Leung Po KinORCID,Levis AviadORCID,Li ZhiyuanORCID,Lico RoccoORCID,Lindahl GregORCID,Lindqvist MichaelORCID,Lisakov MikhailORCID,Liu JunORCID,Liu KuoORCID,Liuzzo ElisabettaORCID,Lo Wen-PingORCID,Lobanov Andrei P.ORCID,Loinard LaurentORCID,Lonsdale Colin J.ORCID,Lu Ru-SenORCID,Mao JirongORCID,Marchili NicolaORCID,Markoff SeraORCID,Marrone Daniel P.ORCID,Marscher Alan P.ORCID,Martí-Vidal IvánORCID,Matsushita SatokiORCID,Matthews Lynn D.ORCID,Medeiros LiaORCID,Menten Karl M.ORCID,Michalik DanielORCID,Mizuno IzumiORCID,Mizuno YosukeORCID,Moran James M.ORCID,Moriyama KotaroORCID,Moscibrodzka MonikaORCID,Müller CorneliaORCID,Mus AlejandroORCID,Musoke GibwaORCID,Myserlis IoannisORCID,Nadolski AndrewORCID,Nagai HiroshiORCID,Nagar Neil M.ORCID,Nakamura MasanoriORCID,Narayan RameshORCID,Narayanan GopalORCID,Natarajan IniyanORCID,Nathanail Antonios,Fuentes Santiago Navarro,Neilsen JoeyORCID,Neri RobertoORCID,Ni ChunchongORCID,Noutsos AristeidisORCID,Nowak Michael A.ORCID,Oh JunghwanORCID,Okino HirokiORCID,Olivares HéctorORCID,Ortiz-León Gisela N.ORCID,Oyama TomoakiORCID,Özel FeryalORCID,Palumbo Daniel C. M.ORCID,Paraschos Georgios FilipposORCID,Park JonghoORCID,Parsons HarrietORCID,Patel NimeshORCID,Pen Ue-LiORCID,Pesce Dominic W.ORCID,Piétu Vincent,Plambeck RichardORCID,PopStefanija Aleksandar,Porth OliverORCID,Pötzl Felix M.ORCID,Prather BenORCID,Preciado-López Jorge A.ORCID,Psaltis DimitriosORCID,Pu Hung-YiORCID,Ramakrishnan VenkatesshORCID,Rao RamprasadORCID,Rawlings Mark G.ORCID,Raymond Alexander W.ORCID,Rezzolla LucianoORCID,Ricarte AngeloORCID,Ripperda BartORCID,Roelofs FreekORCID,Rogers AlanORCID,Ros EduardoORCID,Romero-Cañizales CristinaORCID,Roshanineshat ArashORCID,Rottmann Helge,Roy Alan L.ORCID,Ruiz IgnacioORCID,Ruszczyk ChetORCID,Rygl Kazi L. J.ORCID,Sánchez SalvadorORCID,Sánchez-Argüelles DavidORCID,Sánchez-Portal MiguelORCID,Sasada MahitoORCID,Satapathy KaushikORCID,Savolainen TuomasORCID,Schloerb F. Peter,Schonfeld JonathanORCID,Schuster Karl-FriedrichORCID,Shao LijingORCID,Shen ZhiqiangORCID,Small DesORCID,Sohn Bong WonORCID,SooHoo JasonORCID,Souccar KamalORCID,Sun HeORCID,Tazaki FumieORCID,Tetarenko Alexandra J.ORCID,Tiede PaulORCID,Tilanus Remo P. J.ORCID,Titus MichaelORCID,Torne PabloORCID,Traianou EfthaliaORCID,Trent Tyler,Trippe SaschaORCID,Turk MatthewORCID,van Bemmel IlseORCID,van Langevelde Huib JanORCID,van Rossum Daniel R.ORCID,Vos JesseORCID,Wagner JanORCID,Ward-Thompson DerekORCID,Wardle JohnORCID,Weintroub JonathanORCID,Wex NorbertORCID,Wharton RobertORCID,Wielgus MaciekORCID,Wiik KajORCID,Witzel GuntherORCID,Wondrak Michael F.ORCID,Wong George N.ORCID,Wu QingwenORCID,Yamaguchi PaulORCID,Yoon DoosooORCID,Young AndréORCID,Young KenORCID,Younsi ZiriORCID,Yuan FengORCID,Yuan Ye-FeiORCID,Zensus J. AntonORCID,Zhang ShuoORCID,Zhao Guang-YaoORCID,Zhao Shan-ShanORCID,Agurto Claudio,Araneda Juan Pablo,Arriagada Oriel,Bertarini Alessandra,Berthold Ryan,Blanchard JayORCID,Brown Ken,Cárdenas Mauricio,Cantzler Michael,Caro Patricio,Chuter Tim C.,Ciechanowicz Miroslaw,Coulson Iain M.ORCID,Crowley Joseph,Degenaar NathalieORCID,Dornbusch SvenORCID,Durán Carlos A.ORCID,Forster KarlORCID,Geertsema Gertie,González Edouard,Graham Dave,Gueth Frédéric,Han Chih-Chiang,Herrera Cristian,Herrero-Illana RubenORCID,Heyminck Stefan,Hoge James,Huang Yau-De,Jiang Homin,John David,Klein Thomas,Kubo Derek,Kuroda John,Kwon CalebORCID,Laing RobertORCID,Liu Ching-Tang,Liu Kuan-Yu,Mac-Auliffe Felipe,Martin-Cocher Pierre,Matulonis Callie,Messias HugoORCID,Meyer-Zhao Zheng,Montenegro-Montes FranciscoORCID,Montgomerie William,Muders DirkORCID,Nishioka Hiroaki,Norton Timothy J.,Olivares Rodrigo,Pérez-Beaupuits Juan PabloORCID,Parra Rodrigo,Poirier MichaelORCID,Pradel Nicolas,Raffin Philippe A.,Ramírez Jorge,Reynolds MarkORCID,Saez-Madain Alejandro F.ORCID,Santana Jorge,Silva Kevin M.,Sousa DonORCID,Stahm William,Torstensson Karl,Venegas Paulina,Walther Craig,Wieching Gundolf,Wijnands RudyORCID,Wouterloot Jan G. A.ORCID

Abstract

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.

Publisher

American Astronomical Society

Subject

Space and Planetary Science,Astronomy and Astrophysics

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