摘要
The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5-11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between -2 and -3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*'s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.
| 原文 | 英語 |
|---|---|
| 文章編號 | L19 |
| 期刊 | Astrophysical Journal Letters |
| 卷 | 930 |
| 發行號 | 2 |
| DOIs | |
| 出版狀態 | 已發佈 - 2022 5月 1 |
ASJC Scopus subject areas
- 天文和天體物理學
- 空間與行星科學
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Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign. / Wielgus, Maciek; Marchili, Nicola; Martí-Vidal, Iván 等.
於: Astrophysical Journal Letters, 卷 930, 編號 2, L19, 01.05.2022.研究成果: 雜誌貢獻 › 期刊論文 › 同行評審
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TY - JOUR
T1 - Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign
AU - Wielgus, Maciek
AU - Marchili, Nicola
AU - Martí-Vidal, Iván
AU - Keating, Garrett K.
AU - Ramakrishnan, Venkatessh
AU - Tiede, Paul
AU - Fomalont, Ed
AU - Issaoun, Sara
AU - Neilsen, Joey
AU - Nowak, Michael A.
AU - Blackburn, Lindy
AU - Gammie, Charles F.
AU - Goddi, Ciriaco
AU - Haggard, Daryl
AU - Lee, Daeyoung
AU - Moscibrodzka, Monika
AU - Tetarenko, Alexandra J.
AU - Bower, Geoffrey C.
AU - Chan, Chi Kwan
AU - Chatterjee, Koushik
AU - Chesler, Paul M.
AU - Dexter, Jason
AU - Doeleman, Sheperd S.
AU - Georgiev, Boris
AU - Gurwell, Mark
AU - Johnson, Michael D.
AU - Marrone, Daniel P.
AU - Mus, Alejandro
AU - Psaltis, Dimitrios
AU - Ripperda, Bart
AU - Witzel, Gunther
AU - Akiyama, Kazunori
AU - Alberdi, Antxon
AU - Alef, Walter
AU - Algaba, Juan Carlos
AU - Anantua, Richard
AU - Asada, Keiichi
AU - Azulay, Rebecca
AU - Bach, Uwe
AU - Baczko, Anne Kathrin
AU - Ball, David
AU - Baloković, Mislav
AU - Barrett, John
AU - Bauböck, Michi
AU - Benson, Bradford A.
AU - Bintley, Dan
AU - Blundell, Raymond
AU - Boland, Wilfred
AU - Bouman, Katherine L.
AU - Boyce, Hope
AU - Bremer, Michael
AU - Brinkerink, Christiaan D.
AU - Brissenden, Roger
AU - Britzen, Silke
AU - Broderick, Avery E.
AU - Broguiere, Dominique
AU - Bronzwaer, Thomas
AU - Bustamante, Sandra
AU - Byun, Do Young
AU - Carlstrom, John E.
AU - Ceccobello, Chiara
AU - Chael, Andrew
AU - Chatterjee, Shami
AU - Chen, Ming Tang
AU - Chen, Yongjun
AU - Cho, Ilje
AU - Christian, Pierre
AU - Conroy, Nicholas S.
AU - Conway, John E.
AU - Cordes, James M.
AU - Crawford, Thomas M.
AU - Crew, Geoffrey B.
AU - Cruz-Osorio, Alejandro
AU - Cui, Yuzhu
AU - Davelaar, Jordy
AU - De Laurentis, Mariafelicia
AU - Deane, Roger
AU - Dempsey, Jessica
AU - Desvignes, Gregory
AU - Dhruv, Vedant
AU - Dzib, Sergio A.
AU - Eatough, Ralph P.
AU - Emami, Razieh
AU - Falcke, Heino
AU - Farah, Joseph
AU - Fish, Vincent L.
AU - Ford, H. Alyson
AU - Fraga-Encinas, Raquel
AU - Freeman, William T.
AU - Friberg, Per
AU - Fromm, Christian M.
AU - Fuentes, Antonio
AU - Galison, Peter
AU - García, Roberto
AU - Gentaz, Olivier
AU - Gold, Roman
AU - Gómez-Ruiz, Arturo I.
AU - Gómez, José L.
AU - Gu, Minfeng
AU - Hada, Kazuhiro
AU - Haworth, Kari
AU - Hecht, Michael H.
AU - Hesper, Ronald
AU - Ho, Luis C.
AU - Ho, Paul
AU - Honma, Mareki
AU - Huang, Chih Wei L.
AU - Huang, Lei
AU - Hughes, David H.
AU - Ikeda, Shiro
AU - Impellizzeri, C. M.Violette
AU - Inoue, Makoto
AU - James, David J.
AU - Jannuzi, Buell T.
AU - Janssen, Michael
AU - Jeter, Britton
AU - Jiang, Wu
AU - Jiménez-Rosales, Alejandra
AU - Jorstad, Svetlana
AU - Joshi, Abhishek V.
AU - Jung, Taehyun
AU - Karami, Mansour
AU - Karuppusamy, Ramesh
AU - Kawashima, Tomohisa
AU - Kettenis, Mark
AU - Kim, Dong Jin
AU - Kim, Jae Young
AU - Kim, Jongsoo
AU - Kim, Junhan
AU - Kino, Motoki
AU - Koay, Jun Yi
AU - Kocherlakota, Prashant
AU - Kofuji, Yutaro
AU - Koch, Patrick M.
AU - Koyama, Shoko
AU - Kramer, Carsten
AU - Kramer, Michael
AU - Krichbaum, Thomas P.
AU - Kuo, Cheng Yu
AU - La Bella, Noemi
AU - Lauer, Tod R.
AU - Lee, Sang Sung
AU - Leung, Po Kin
AU - Levis, Aviad
AU - Li, Zhiyuan
AU - Lico, Rocco
AU - Lindahl, Greg
AU - Lindqvist, Michael
AU - Lisakov, Mikhail
AU - Liu, Jun
AU - Liu, Kuo
AU - Liuzzo, Elisabetta
AU - Lo, Wen Ping
AU - Lobanov, Andrei P.
AU - Loinard, Laurent
AU - Lonsdale, Colin
AU - Lu, Ru Sen
AU - Mao, Jirong
AU - Markoff, Sera
AU - Marscher, Alan P.
AU - Matsushita, Satoki
AU - Matthews, Lynn D.
AU - Medeiros, Lia
AU - Menten, Karl M.
AU - Michalik, Daniel
AU - Mizuno, Izumi
AU - Mizuno, Yosuke
AU - Moran, James M.
AU - Moriyama, Kotaro
AU - Müller, Cornelia
AU - Musoke, Gibwa
AU - Myserlis, Ioannis
AU - Nadolski, Andrew
AU - Nagai, Hiroshi
AU - Nagar, Neil M.
AU - Nakamura, Masanori
AU - Narayan, Ramesh
AU - Narayanan, Gopal
AU - Natarajan, Iniyan
AU - Nathanail, Antonios
AU - Fuentes, Santiago Navarro
AU - Neri, Roberto
AU - Ni, Chunchong
AU - Noutsos, Aristeidis
AU - Oh, Junghwan
AU - Okino, Hiroki
AU - Olivares, Héctor
AU - Ortiz-León, Gisela N.
AU - Oyama, Tomoaki
AU - Özel, Feryal
AU - Palumbo, Daniel C.M.
AU - Paraschos, Georgios Filippos
AU - Park, Jongho
AU - Parsons, Harriet
AU - Patel, Nimesh
AU - Pen, Ue Li
AU - Pesce, Dominic W.
AU - Piétu, Vincent
AU - Plambeck, Richard
AU - PopStefanija, Aleksandar
AU - Porth, Oliver
AU - Pötzl, Felix M.
AU - Prather, Ben
AU - Preciado-López, Jorge A.
AU - Pu, Hung Yi
AU - Rao, Ramprasad
AU - Rawlings, Mark G.
AU - Raymond, Alexander W.
AU - Rezzolla, Luciano
AU - Ricarte, Angelo
AU - Roelofs, Freek
AU - Rogers, Alan
AU - Ros, Eduardo
AU - Romero-Canizales, Cristina
AU - Roshanineshat, Arash
AU - Rottmann, Helge
AU - Roy, Alan L.
AU - Ruiz, Ignacio
AU - Ruszczyk, Chet
AU - Rygl, Kazi L.J.
AU - Sánchez, Salvador
AU - Sánchez-Argüelles, David
AU - Sánchez-Portal, Miguel
AU - Sasada, Mahito
AU - Satapathy, Kaushik
AU - Savolainen, Tuomas
AU - Schloerb, F. Peter
AU - Schuster, Karl Friedrich
AU - Shao, Lijing
AU - Shen, Zhiqiang
AU - Small, Des
AU - Sohn, Bong Won
AU - SooHoo, Jason
AU - Souccar, Kamal
AU - Sun, He
AU - Tazaki, Fumie
AU - Tilanus, Remo P.J.
AU - Titus, Michael
AU - Torne, Pablo
AU - Traianou, Efthalia
AU - Trent, Tyler
AU - Trippe, Sascha
AU - van Bemmel, Ilse
AU - van Langevelde, Huib Jan
AU - van Rossum, Daniel R.
AU - Vos, Jesse
AU - Wagner, Jan
AU - Ward-Thompson, Derek
AU - Wardle, John
AU - Weintroub, Jonathan
AU - Wex, Norbert
AU - Wharton, Robert
AU - Wiik, Kaj
AU - Wondrak, Michael F.
AU - Wong, George N.
AU - Wu, Qingwen
AU - Yamaguchi, Paul
AU - Yoon, Doosoo
AU - Young, André
AU - Yuan, Feng
AU - Young, Ken
AU - Younsi, Ziri
AU - Yuan, Ye Fei
AU - Zensus, J. Anton
AU - Zhang, Shuo
AU - Zhao, Guang Yao
AU - Zhao, Shan Shan
N1 - Funding Information: We thank Yuhei Iwata, Lena Murchikova, Rebecca Phillipson, and Chris White for comments and discussions, as well as Alexandra Elbakyan for her contributions to the open science initiative. We also thank the anonymous ApJL referee for helpful and constructive comments. The Event Horizon Telescope Collaboration thanks the following organizations and programs: National Science Foundation (awards OISE-1743747, AST-1816420, AST-1716536, AST-1440254, AST-1935980); 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); NASA Hubble Fellowship grant HST-HF2-51431.001-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 Academy of Finland (projects 274477, 284495, 312496, 315721); the Agencia Nacional de Investigación y Desarrollo (ANID), Chile via NCN19_058 (TITANs) and Fondecyt 3190878, 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 China Scholarship Council; Consejo Nacional de Ciencia y Tecnología (CONACYT, Mexico, projects U0004-246083, U0004-259839, F0003-272050, M0037-279006, F0003-281692, 104497, 275201, 263356); 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 European Research Council Synergy Grant “BlackHoleCam: Imaging the Event Horizon of Black Holes” (grant 610058); the Generalitat Valenciana postdoctoral grant APOSTD/2018/177 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 Istituto Nazionale di Fisica Nucleare (INFN) sezione di Napoli, iniziative specifiche TEONGRAV; the two Dutch National Supercomputers, Cartesius and Snellius (NWO grant 2021.013); 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 Princeton/Flatiron and Joint Columbia/Flatiron Postdoctoral Fellowships, with research at the Flatiron Institute supported by the Simons Foundation; the Japanese Government (Monbukagakusho: MEXT) Scholarship; the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for JSPS Research Fellowship (JP17J08829); the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS, grants QYZDJ-SSW-SLH057, QYZDJ-SSW-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, 18K03709, 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); the National Institute of Natural Sciences (NINS) of Japan; the National Key Research and Development Program of China (grants 2016YFA0400704 and 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-1555365, AST-1615796, AST-1715061, AST-1716327, AST-1903847, AST-2034306); the Natural Science Foundation of China (grants 11650110427, 10625314, 11721303, 11725312, 11933007, 11991052, 11991053); NWO grant No. OCENW. KLEIN.113; a fellowship of China Postdoctoral Science Foundation (2020M671266); 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, 2015-R1D1A1A01056807; the Korea Research Fellowship Program: NRF-2015H1D3A1066561, Basic Research Support Grant 2019R1F1A1059721); the Netherlands Organization for Scientific Research (NWO) VICI award (grant 639.043.513) and Spinoza Prize SPI 78-409; the New Scientific Frontiers with Precision Radio Interferometry Fellowship awarded by the South African Radio Astronomy Observatory (SARAO), which is a facility of the National Research Foundation (NRF), an agency of the Department of Science and Technology (DST) of South Africa; the 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 Spanish Ministerio de Ciencia e Innovaci-n (grants PGC2018-098915-B-C21, AYA2016-80889-P, PID2019-108995GB-C21, PID2020-117404GB-C21); 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 Toray Science Foundation; 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 M2FINDERS project, which has received funding by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant agreement No. 101018682); 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); the European Union's Horizon 2020 research and innovation program under grant agreement No. 730562 RadioNet; Shanghai Pilot Program for Basic Research, Chinese Academy of Science, Shanghai Branch (JCYJ-SHFY-2021-013); ALMA North America Development Fund; the Academia Sinica; Chandra DD7-18089X and TM6-17006X; and the GenT Program (Generalitat Valenciana) Project CIDEGENT/2018/021. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), supported by NSF grant ACI-1548562, and CyVerse, supported by NSF grants DBI-0735191, DBI-1265383, and DBI-1743442. XSEDE Stampede2 resource at TACC was allocated through TG-AST170024 and TG-AST080026N. XSEDE JetStream resource at PTI and TACC was allocated through AST170028. The simulations were performed in part on the SuperMUC cluster at the LRZ in Garching, on the LOEWE cluster in CSC in Frankfurt, and on the HazelHen cluster at the HLRS in Stuttgart. This research was enabled in part by support provided by Compute Ontario (http://computeontario.ca), Calcul Quebec (http://www.calculquebec.ca), and Compute Canada (http://www.computecanada.ca). C.C. acknowledges support from the Swedish Research Council (VR). We thank the staff at the participating observatories, correlation centers, and institutions for their enthusiastic support. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.01154.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 NRAO is a facility of the NSF operated under cooperative agreement by AUI. Support for this work was also provided by the NASA Hubble Fellowship grant HST-HF2-51431.001-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. Hector Olivares and Gibwa Musoke were supported by Virtual Institute of Accretion (VIA) postdoctoral fellowships from the Netherlands Research School for Astronomy (NOVA). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie (Germany), ESO, and the Onsala Space Observatory (Sweden). 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 R&D Program (No. 2017YFA0402700) of China. Additional funding support for the JCMT is provided by the Science and Technologies Facility Council (UK) and participating universities in the UK and Canada. Simulations were performed in part on the SuperMUC cluster at the LRZ in Garching, on the LOEWE cluster in CSC in Frankfurt, on the HazelHen cluster at the HLRS in Stuttgart, and on the Pi2.0 and Siyuan Mark-I at Shanghai Jiao Tong University. The computer resources of the Finnish IT Center for Science (CSC) and the Finnish Computing Competence Infrastructure (FCCI) project are acknowledged. Junghwan Oh was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2021R1A6A3A01086420). We thank Martin Shepherd for the addition of extra features in the Difmap software that were used for the CLEAN imaging results presented in this paper. The computing cluster of Shanghai VLBI correlator supported by the Special Fund for Astronomy from the Ministry of Finance in China is acknowledged. The LMT is a project operated by the Instituto Nacional de Astrífisica, Óptica, y Electrínica (Mexico) and the University of Massachusetts at Amherst (USA). 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 Geogrífico Nacional, Spain). 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. Support for this work was provided by NASA through the NASA Hubble Fellowship grant No. HST-HF2ers. This research has made use of NASA's Astrophysics Data System. We gratefully acknowledge the support provided by the extended staff-51494.001 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 EHTC has received generous donations of FPGA chips from Xilinx Inc., under the Xilinx University Program. The EHTC has benefited from technology shared under 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 Mas 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. We acknowledge the significance that Maunakea, where the SMA and JCMT EHT stations are located, has for the indigenous Hawaiian people. Publisher Copyright: © 2022. The Author(s)
PY - 2022/5/1
Y1 - 2022/5/1
N2 - The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5-11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between -2 and -3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*'s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.
AB - The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5-11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between -2 and -3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*'s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.
UR - http://www.scopus.com/inward/record.url?scp=85130735318&partnerID=8YFLogxK
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U2 - 10.3847/2041-8213/ac6428
DO - 10.3847/2041-8213/ac6428
M3 - Article
AN - SCOPUS:85130735318
VL - 930
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
SN - 2041-8205
IS - 2
M1 - L19
ER -