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Published December 10, 2023 | Published
Journal Article Open

A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set

Torne, Pablo ORCID icon
Liu, Kuo ORCID icon
Eatough, Ralph P. ORCID icon
Wongphechauxsorn, Jompoj ORCID icon
Cordes, James M. ORCID icon
Desvignes, Gregory ORCID icon
De Laurentis, Mariafelicia ORCID icon
Kramer, Michael ORCID icon
Ransom, Scott M. ORCID icon
Chatterjee, Shami ORCID icon
Wharton, Robert ORCID icon
Karuppusamy, Ramesh ORCID icon
Blackburn, Lindy ORCID icon
Janssen, Michael ORCID icon
Chan, Chi-kwan ORCID icon
Crew, Geoffrey, B. ORCID icon
Matthews, Lynn D. ORCID icon
Goddi, Ciriaco ORCID icon
Rottmann, Helge ORCID icon
Wagner, Jan ORCID icon
Sánchez, Salvador ORCID icon
Ruiz, Ignacio ORCID icon
Abbate, Federico ORCID icon
Bower, Geoffrey C. ORCID icon
Salamanca, Juan J. ORCID icon
Gómez-Ruiz, Arturo I. ORCID icon
Herrera-Aguilar, Alfredo ORCID icon
Jiang 江, Wu 悟 ORCID icon
Lu 路, Ru-Sen 如森 ORCID icon
Pen, Ue-Li ORCID icon
Raymond, Alexander W. ORCID icon
Shao, Lijing ORCID icon
Shen 沈, Zhiqiang 志强 ORCID icon
Paubert, Gabriel
Sanchez-Portal, Miguel ORCID icon
Kramer, Carsten ORCID icon
Castillo, Manuel
Navarro, Santiago
John, David
Schuster, Karl-Friedrich ORCID icon
Johnson, Michael D. ORCID icon
Rygl, Kazi L. J. ORCID icon
Akiyama, Kazunori ORCID icon
Alberdi, Antxon ORCID icon
Alef, Walter
Algaba, Juan Carlos ORCID icon
Anantua, Richard ORCID icon
Asada, Keiichi ORCID icon
Azulay, Rebecca ORCID icon
Bach, Uwe ORCID icon
Baczko, Anne-Kathrin ORCID icon
Ball, David
Baloković, Mislav ORCID icon
Barrett, John ORCID icon
Bauböck, Michi ORCID icon
Benson, Bradford A. ORCID icon
Bintley, Dan
Blundell, Raymond ORCID icon
Bouman, Katherine L.1 ORCID icon
Boyce, Hope ORCID icon
Bremer, Michael
Brinkerink, Christiaan D. ORCID icon
Brissenden, Roger ORCID icon
Britzen, Silke ORCID icon
Broderick, Avery E. ORCID icon
Broguiere, Dominique ORCID icon
Bronzwaer, Thomas ORCID icon
Bustamante, Sandra ORCID icon
Byun, Do-Young ORCID icon
Carlstrom, John E. ORCID icon
Ceccobello, Chiara ORCID icon
Chael, Andrew ORCID icon
Chang, Dominic O. ORCID icon
Chatterjee, Koushik ORCID icon
Chen, Ming-Tang ORCID icon
Chen 陈, Yongjun 永军 ORCID icon
Cheng, Xiaopeng ORCID icon
Cho, Ilje ORCID icon
Christian, Pierre ORCID icon
Conroy, Nicholas S. ORCID icon
Conway, John E. ORCID icon
Crawford, Thomas M. ORCID icon
Cruz-Osorio, Alejandro ORCID icon
Cui 崔, Yuzhu 玉竹 ORCID icon
Dahale, Rohan ORCID icon
Davelaar, Jordy ORCID icon
Deane, Roger ORCID icon
Dempsey, Jessica ORCID icon
Dexter, Jason ORCID icon
Dhruv, Vedant ORCID icon
Doeleman, Sheperd S. ORCID icon
Dougal, Sean ORCID icon
Dzib, Sergio A. ORCID icon
Emami, Razieh ORCID icon
Falcke, Heino ORCID icon
Farah, Joseph ORCID icon
Fish, Vincent L. ORCID icon
Fomalont, Ed ORCID icon
Ford, H. Alyson ORCID icon
Foschi, Marianna ORCID icon
Fraga-Encinas, Raquel ORCID icon
Freeman, William T.
Friberg, Per ORCID icon
Fromm, Christian M. ORCID icon
Fuentes, Antonio ORCID icon
Galison, Peter ORCID icon
Gammie, Charles F. ORCID icon
García, Roberto ORCID icon
Gentaz, Olivier ORCID icon
Georgiev, Boris ORCID icon
Gold, Roman ORCID icon
Gómez, José L. ORCID icon
Gu 顾, Minfeng 敏峰 ORCID icon
Gurwell, Mark ORCID icon
Hada, Kazuhiro ORCID icon
Haggard, Daryl ORCID icon
Haworth, Kari
Hecht, Michael H. ORCID icon
Hesper, Ronald ORCID icon
Heumann, Dirk ORCID icon
Ho 何, Luis C. 子山 ORCID icon
Ho, Paul ORCID icon
Honma, Mareki ORCID icon
Huang, Chih-Wei L. ORCID icon
Huang 黄, Lei 磊 ORCID icon
Hughes, David H.
Ikeda, Shiro ORCID icon
Impellizzeri, C. M. Violette ORCID icon
Inoue, Makoto ORCID icon
Issaoun, Sara ORCID icon
James, David J. ORCID icon
Jannuzi, Buell T. ORCID icon
Jeter, Britton ORCID icon
Jiménez-Rosales, Alejandra ORCID icon
Jorstad, Svetlana ORCID icon
Joshi, Abhishek V. ORCID icon
Jung, Taehyun ORCID icon
Karami, Mansour ORCID icon
Kawashima, Tomohisa ORCID icon
Keating, Garrett K. ORCID icon
Kettenis, Mark ORCID icon
Kim, Dong-Jin ORCID icon
Kim, Jae-Young ORCID icon
Kim, Jongsoo ORCID icon
Kim, Junhan ORCID icon
Kino, Motoki ORCID icon
Koay, Jun Yi ORCID icon
Kocherlakota, Prashant ORCID icon
Kofuji, Yutaro
Koyama, Shoko ORCID icon
Krichbaum, Thomas P. ORCID icon
Kuo, Cheng-Yu ORCID icon
La Bella, Noemi ORCID icon
Lauer, Tod R. ORCID icon
Lee, Daeyoung ORCID icon
Lee, Sang-Sung ORCID icon
Leung, Po Kin ORCID icon
Levis, Aviad ORCID icon
Li 李, Zhiyuan 志远 ORCID icon
Lico, Rocco ORCID icon
Lindahl, Greg ORCID icon
Lindqvist, Michael ORCID icon
Lisakov, Mikhail ORCID icon
Liu 刘, Jun 俊 ORCID icon
Liuzzo, Elisabetta ORCID icon
Lo, Wen-Ping ORCID icon
Lobanov, Andrei P. ORCID icon
Loinard, Laurent ORCID icon
Lonsdale, Colin J. ORCID icon
MacDonald, Nicholas R. ORCID icon
Mao 毛, Jirong 基荣 ORCID icon
Marchili, Nicola ORCID icon
Markoff, Sera ORCID icon
Marrone, Daniel P. ORCID icon
Marscher, Alan P. ORCID icon
Martí-Vidal, Iván ORCID icon
Matsushita, Satoki ORCID icon
Medeiros, Lia ORCID icon
Menten, Karl M. ORCID icon
Michalik, Daniel ORCID icon
Mizuno, Izumi ORCID icon
Mizuno, Yosuke ORCID icon
Moran, James M. ORCID icon
Moriyama, Kotaro ORCID icon
Moscibrodzka, Monika ORCID icon
Müller, Cornelia ORCID icon
Müller, Hendrik ORCID icon
Mus, Alejandro ORCID icon
Musoke, Gibwa ORCID icon
Myserlis, Ioannis ORCID icon
Nadolski, Andrew ORCID icon
Nagai, Hiroshi ORCID icon
Nagar, Neil M. ORCID icon
Nakamura, Masanori ORCID icon
Narayan, Ramesh ORCID icon
Narayanan, Gopal ORCID icon
Natarajan, Iniyan ORCID icon
Nathanail, Antonios ORCID icon
Neilsen, Joey ORCID icon
Neri, Roberto ORCID icon
Ni, Chunchong ORCID icon
Noutsos, Aristeidis ORCID icon
Nowak, Michael A. ORCID icon
Oh, Junghwan ORCID icon
Okino, Hiroki ORCID icon
Olivares, Héctor ORCID icon
Ortiz-León, Gisela N. ORCID icon
Oyama, Tomoaki ORCID icon
Özel, Feryal ORCID icon
Palumbo, Daniel C. M. ORCID icon
Paraschos, Georgios Filippos ORCID icon
Park, Jongho ORCID icon
Parsons, Harriet ORCID icon
Patel, Nimesh ORCID icon
Pesce, Dominic W. ORCID icon
Piétu, Vincent
Plambeck, Richard ORCID icon
PopStefanija, Aleksandar
Porth, Oliver ORCID icon
Pötzl, Felix M. ORCID icon
Prather, Ben ORCID icon
Preciado-López, Jorge A. ORCID icon
Psaltis, Dimitrios ORCID icon
Pu, Hung-Yi ORCID icon
Ramakrishnan, Venkatessh ORCID icon
Rao, Ramprasad ORCID icon
Rawlings, Mark G. ORCID icon
Rezzolla, Luciano ORCID icon
Ricarte, Angelo ORCID icon
Ripperda, Bart ORCID icon
Roelofs, Freek ORCID icon
Rogers, Alan ORCID icon
Ros, Eduardo ORCID icon
Romero-Cañizales, Cristina ORCID icon
Roshanineshat, Arash ORCID icon
Roy, Alan L. ORCID icon
Ruszczyk, Chet ORCID icon
Sánchez-Argüelles, David ORCID icon
Sasada, Mahito ORCID icon
Satapathy, Kaushik ORCID icon
Savolainen, Tuomas ORCID icon
Schloerb, F. Peter ORCID icon
Schonfeld, Jonathan ORCID icon
Small, Des ORCID icon
Sohn, Bong Won ORCID icon
SooHoo, Jason ORCID icon
Souccar, Kamal ORCID icon
Sun 孙, He 赫 ORCID icon
Tetarenko, Alexandra J. ORCID icon
Tiede, Paul ORCID icon
Tilanus, Remo P. J. ORCID icon
Titus, Michael ORCID icon
Toscano, Teresa ORCID icon
Traianou, Efthalia ORCID icon
Trent, Tyler ORCID icon
Trippe, Sascha ORCID icon
Turk, Matthew ORCID icon
van Bemmel, Ilse ORCID icon
van Langevelde, Huib Jan ORCID icon
van Rossum, Daniel R. ORCID icon
Vos, Jesse ORCID icon
Ward-Thompson, Derek ORCID icon
Wardle, John ORCID icon
Weintroub, Jonathan ORCID icon
Wex, Norbert ORCID icon
Wielgus, Maciek ORCID icon
Wiik, Kaj ORCID icon
Witzel, Gunther ORCID icon
Wondrak, Michael F. ORCID icon
Wong, George N. ORCID icon
Wu 吴, Qingwen 庆文 ORCID icon
Yadlapalli, Nitika ORCID icon
Yamaguchi, Paul ORCID icon
Yfantis, Aristomenis ORCID icon
Yoon, Doosoo ORCID icon
Young, André ORCID icon
Young, Ken ORCID icon
Younsi, Ziri ORCID icon
Yu 于, Wei 威 ORCID icon
Yuan 袁, Feng 峰 ORCID icon
Yuan 袁, Ye-Fei 业飞 ORCID icon
Zensus, J. Anton ORCID icon
Zhang, Shuo ORCID icon
Zhao, Guang-Yao ORCID icon
Zhao 赵, Shan-Shan 杉杉 ORCID icon
  • 1. ROR icon California Institute of Technology

Abstract

In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz (λ = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars—which typically exhibit steep emission spectra—are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (≲2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.

Copyright and License

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We are grateful to the anonymous referee for the review and providing suggestions that improved the manuscript. We thank the staff at the participating observatories and correlator centers that made possible the EHT 2017 observations. P.T. thanks Pablo Mellado and William Robertson for their support through several stages of the data reduction in the IRAM servers. R.P.E. is funded by the Chinese Academy of Sciences President's International Fellowship Initiative, grant No. 2021FSM0004. S.M.R. is a CIFAR Fellow and is supported by the NSF Physics Frontiers Center awards 1430284 and 2020265. This work was supported by the European Research Council Synergy Grant "BlackHoleCam: Imaging the Event Horizon of Black Holes" (grant 610058). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.01404.V. ALMA is a partnership of the European Southern Observatory (ESO; Europe, representing its member states), NSF, and National Institutes of Natural Sciences of Japan, together with National Research Council (Canada), Ministry of Science and Technology (MOST; Taiwan), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA; Taiwan), and Korea Astronomy and Space Science Institute (KASI; Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, Associated Universities, Inc. (AUI)/NRAO, and the National Astronomical Observatory of Japan (NAOJ). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The LMT is a project operated by the Instituto Nacional de Astrófisica, Óptica, y Electrónica (Mexico) and the University of Massachusetts at Amherst (USA). This work is partly based on observations carried out with the IRAM 30 m Telescope under project No. 084-17. The IRAM 30 m Telescope on Pico Veleta, Spain is operated by IRAM and supported by CNRS (Centre National de la Recherche Scientifique, France), MPG (Max-Planck-Gesellschaft, Germany), and IGN (Instituto Geográfico Nacional, Spain). This research has made use of NASA's Astrophysics Data System Bibliographic Services. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The Event Horizon Telescope Collaboration thanks the following organizations and programs: the Academia Sinica; the Academy of Finland (projects 274477, 284495, 312496, and 315721); the Agencia Nacional de Investigación y Desarrollo (ANID), Chile via NCN19_058 (TITANs) and Fondecyt 1221421, the Alexander von Humboldt Stiftung; an Alfred P. Sloan Research Fellowship; Allegro, the European ALMA Regional Centre node in the Netherlands, the NL astronomy research network NOVA and the astronomy institutes of the University of Amsterdam, Leiden University and Radboud University; the ALMA North America Development Fund; the Astrophysics and High Energy Physics program by MCIN (with funding from European Union NextGenerationEU, PRTR-C17I1); the Black Hole Initiative, which is funded by grants from the John Templeton Foundation and the Gordon and Betty Moore Foundation (although the opinions expressed in this work are those of the author(s) and do not necessarily reflect the views of these Foundations); the Brinson Foundation; Chandra DD7-18089X and TM6-17006X; the China Scholarship Council; the China Postdoctoral Science Foundation fellowships (2020M671266, 2022M712084); Consejo Nacional de Ciencia y Tecnología (CONACYT, Mexico, projects U0004-246083, U0004-259839, F0003-272050, M0037-279006, F0003-281692, 104497, 275201, and 263356); the Consejería de Economía, Conocimiento, Empresas y Universidad of the Junta de Andalucía (grant P18-FR-1769), the Consejo Superior de Investigaciones Científicas (grant 2019AEP112); the Delaney Family via the Delaney Family John A. Wheeler Chair at Perimeter Institute; Dirección General de Asuntos del Personal Académico-Universidad Nacional Autónoma de México (DGAPA-UNAM, projects IN112417 and IN112820); the Dutch Organization for Scientific Research (NWO) for VICI award (grant 639.043.513), grant OCENW.KLEIN.113 and the Dutch black hole Consortium (with project No. NWA 1292.19.202) of the research program the National Science Agenda; the Dutch National Supercomputers, Cartesius and Snellius (NWO grant 2021.013); the EACOA Fellowship awarded by the East Asia Core Observatories Association, which consists of the Academia Sinica Institute of Astronomy and Astrophysics, the National Astronomical Observatory of Japan, Center for Astronomical Mega-Science, Chinese Academy of Sciences, and the Korea Astronomy and Space Science Institute; the European Union Horizon 2020 research and innovation program under grant agreements RadioNet (No 730562) and M2FINDERS (No 101018682); the Horizon ERC Grants 2021 program under grant agreement No. 101040021; the Generalitat Valenciana (grants APOSTD/2018/177 and ASFAE/2022/018) and GenT Program (project CIDEGENT/2018/021); MICINN Research Project PID2019-108995GB-C22; the European Research Council for advanced grant "JETSET: Launching, propagation and emission of relativistic jets from binary mergers and across mass scales" (grant No. 884631); the Institute for Advanced Study; the Istituto Nazionale di Fisica Nucleare (INFN) sezione di Napoli, iniziative specifiche TEONGRAV; the International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne; DFG research grant "Jet physics on horizon scales and beyond" (grant No. FR 4069/2-1); Joint Columbia/Flatiron Postdoctoral Fellowship, research at the Flatiron Institute is supported by the Simons Foundation; the Japan Ministry of Education, Culture, Sports, Science and Technology (MEXT; grant JPMXP1020200109); the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for JSPS Research Fellowship (JP17J08829); the Joint Institute for Computational Fundamental Science, Japan; the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS, grants QYZDJ-SSW-SLH057, QYZDJSSW-SYS008, ZDBS-LY-SLH011); the Leverhulme Trust Early Career Research Fellowship; the Max-Planck-Gesellschaft (MPG); the Max Planck Partner Group of the MPG and the CAS; the MEXT/JSPS KAKENHI (grants 18KK0090, JP21H01137, JP18H03721, JP18K13594, 18K03709, JP19K14761, 18H01245, 25120007); the Malaysian Fundamental Research Grant Scheme (FRGS) FRGS/1/2019/STG02/UM/02/6; the MIT International Science and Technology Initiatives (MISTI) Funds; the Ministry of Science and Technology (MOST) of Taiwan (103-2119-M-001-010-MY2, 105-2112-M-001-025-MY3, 105-2119-M-001-042, 106-2112-M-001-011, 106-2119-M-001-013, 106-2119-M-001-027, 106-2923-M-001-005, 107-2119-M-001-017, 107-2119-M-001-020, 107-2119-M-001-041, 107-2119-M-110-005, 107-2923-M-001-009, 108-2112-M-001-048, 108-2112-M-001-051, 108-2923-M-001-002, 109-2112-M-001-025, 109-2124-M-001-005, 109-2923-M-001-001, 110-2112-M-003-007-MY2, 110-2112-M-001-033, 110-2124-M-001-007, and 110-2923-M-001-001); the Ministry of Education (MoE) of Taiwan Yushan Young Scholar Program; the Physics Division, National Center for Theoretical Sciences of Taiwan; the National Aeronautics and Space Administration (NASA, Fermi Guest Investigator grant 80NSSC20K1567, NASA Astrophysics Theory Program grant 80NSSC20K0527, NASA NuSTAR award 80NSSC20K0645); NASA Hubble Fellowship grants HST-HF2-51431.001-A, HST-HF2-51482.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555; the National Institute of Natural Sciences (NINS) of Japan; the National Key Research and Development Program of China (grant 2016YFA0400704, 2017YFA0402703, 2016YFA0400702); the National Science Foundation (NSF, grants AST-0096454, AST-0352953, AST-0521233, AST-0705062, AST-0905844, AST-0922984, AST-1126433, AST-1140030, DGE-1144085, AST-1207704, AST-1207730, AST-1207752, MRI-1228509, OPP-1248097, AST-1310896, AST-1440254, AST-1555365, AST-1614868, AST-1615796, AST-1715061, AST-1716327, AST-1716536, OISE-1743747, AST-1816420, AST-1935980, AST-2034306); NSF Astronomy and Astrophysics Postdoctoral Fellowship (AST-1903847); the Natural Science Foundation of China (grants 11650110427, 10625314, 11721303, 11725312, 11873028, 11933007, 11991052, 11991053, 12192220, 12192223); the Natural Sciences and Engineering Research Council of Canada (NSERC, including a Discovery Grant and the NSERC Alexander Graham Bell Canada Graduate Scholarships-Doctoral Program); the National Youth Thousand Talents Program of China; the National Research Foundation of Korea (the Global PhD Fellowship Grant: grants NRF-2015H1A2A1033752, the Korea Research Fellowship Program: NRF-2015H1D3A1066561, Brain Pool Program: 2019H1D3A1A01102564, Basic Research Support Grant 2019R1F1A1059721, 2021R1A6A3A01086420, 2022R1C1C1005255); Netherlands Research School for Astronomy (NOVA) Virtual Institute of Accretion (VIA) postdoctoral fellowships; Onsala Space Observatory (OSO) national infrastructure, for the provisioning of its facilities/observational support (OSO receives funding through the Swedish Research Council under grant 2017-00648); the Perimeter Institute for Theoretical Physics (research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development and by the Province of Ontario through the Ministry of Research, Innovation and Science); the Princeton Gravity Initiative; the Spanish Ministerio de Ciencia e Innovación (grants PGC2018-098915-B-C21, AYA2016-80889-P, PID2019-108995GB-C21, and PID2020-117404GB-C21); the University of Pretoria for financial aid in the provision of the new Cluster Server nodes and SuperMicro (USA) for an SEEDING grant approved toward these nodes in 2020; the Shanghai Pilot Program for Basic Research, Chinese Academy of Science, Shanghai Branch (JCYJ-SHFY-2021-013); the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709); the Spinoza Prize SPI 78-409; the South African Research Chairs Initiative, through the South African Radio Astronomy Observatory (SARAO, grant ID 77948), which is a facility of the National Research Foundation (NRF), an agency of the Department of Science and Innovation (DSI) of South Africa; the Toray Science Foundation; the Swedish Research Council (VR); the US Department of Energy (USDOE) through the Los Alamos National Laboratory (operated by Triad National Security, LLC, for the National Nuclear Security Administration of the USDOE (contract 89233218CNA000001); and the YCAA Prize Postdoctoral Fellowship. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under contract No. DE-AC05-00OR22725. We also thank the Center for Computational Astrophysics, National Astronomical Observatory of Japan. The computing cluster of Shanghai VLBI correlator supported by the Special Fund for Astronomy from the Ministry of Finance in China is acknowledged. This work was partially supported by FAPESP (Fundação de Amparo á Pesquisa do Estado de São Paulo) under grant 2021/01183-8. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie (Germany), ESO, and the Onsala Space Observatory (Sweden). The SMT is operated by the Arizona Radio Observatory, a part of the Steward Observatory of the University of Arizona, with financial support of operations from the State of Arizona and financial support for instrumentation development from the NSF. Support for SPT participation in the EHT is provided by the National Science Foundation through award OPP-1852617 to the University of Chicago. Partial support is also provided by the Kavli Institute of Cosmological Physics at the University of Chicago. The SPT hydrogen maser was provided on loan from the GLT, courtesy of ASIAA. The SMA is a joint project between the SAO and ASIAA and is funded by the Smithsonian Institution and the Academia Sinica. The JCMT is operated by the East Asian Observatory on behalf of the NAOJ, ASIAA, and KASI, as well as the Ministry of Finance of China, Chinese Academy of Sciences, and the National Key Research and Development Program (No. 2017YFA0402700) of China and Natural Science Foundation of China grant 11873028. Additional funding support for the JCMT is provided by the Science and Technologies Facility Council (UK) and participating universities in the UK and Canada. We acknowledge the significance that Maunakea, where the SMA and JCMT EHT stations are located, has for the indigenous Hawaiian people. The EHTC has received generous donations of FPGA chips from Xilinx Inc., under the Xilinx University Program. The EHTC has benefited from technology shared under an open-source license by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER). The EHT project is grateful to T4Science and Microsemi for their assistance with Hydrogen Masers. We gratefully acknowledge the support provided by the extended staff of the ALMA, both from the inception of the ALMA Phasing Project through the observational campaigns of 2017 and 2018. We would like to thank A. Deller and W. Brisken for EHT-specific support with the use of DiFX.

Facilities

ALMA - Atacama Large Millimeter Array, LMT - , IRAM:30m - Institute de Radioastronomie Millimetrique 30 meter telescope

Software References

MPIvdif2psrfits, presto (Ransom 2011), riptide (Morello et al. 2020), numpy (Harris et al. 2020), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), tempo (Nice et al. 2015), sigpyproc (Lorimer 2011)

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Additional details

Created:
January 4, 2024
Modified:
January 4, 2024