Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign
Journal article, 2026
Context. Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, provides a unique laboratory to study accretion dynamics and plasma processes near the event horizon. Aims. We investigated the variability and polarization properties of Sgr A* using ALMA observations during the 2018 Event Horizon Telescope campaign. Methods. We analyzed high-cadence full-polarization light curves from ALMA at millimeter wavelengths, performed time-series analysis, and investigated the temporal behavior during an X-ray flare observed by Chandra on 2018 April 24. The variability characteristics are compared with expectations from standard accretion flow models. Results. We find low variability in total intensity (sigma/mu < 10%), but significantly higher variability in linear and circular polarization ( similar to 30% and similar to 50%, respectively). A time-series analysis reveals red-noise variability, with power spectral densities between 2 and 3 across all Stokes parameters. Polarized intensity shows stable intra-day timescales, while total intensity exhibits more variable timescales, suggesting distinct emission regions, with polarization likely arising from a coherent structure. On April 24, a statistically significant inter-band delay in polarized intensity coincides with a near-simultaneous X-ray and millimeter peak that deviates from the typical delayed flare scenario. This event also features enhanced millimeter variability and coherent polarization loop evolution. The observed simultaneity challenges standard models of transient synchrotron emission with cooling delays, favoring instead a scenario of continuous energy injection in an optically thin region. Conclusions. Our results offer new constraints on the physical mechanisms driving variability in Sgr A*, and provide key observational input for refining theoretical models of accretion and plasma behavior in the vicinity of supermassive black holes.
techniques: interferometric
Galaxy: center
techniques: polarimetric
black hole physics
Author
Ezequiel Albentosa-Ruiz
Universitat de Valencia
Jasmin E. Washington
University of Arizona
Nicola Marchili
Istituto nazionale di astrofisica (INAF)
Max Planck Society
Italian ALMA Regional Centre
Ivan Marti-Vidal
Universitat de Valencia
Ciriaco Goddi
University of Sao Paulo (USP)
National Institute for Nuclear Physics
Istituto nazionale di astrofisica (INAF)
University of Cagliari
Maciek Wielgus
Spanish National Research Council (CSIC)
Alejandro Mus
Italian ALMA Regional Centre
University of Cagliari
Istituto nazionale di astrofisica (INAF)
Angelo Ricarte
Harvard University
Harvard-Smithsonian Center for Astrophysics
Daniel P. Marrone
University of Arizona
Leon D. S. Salas
University of Amsterdam
Yuhei Iwata
National Astronomical Observatory of Japan
Douglas F. Carlos
University of Sao Paulo (USP)
Alexandra J. Tetarenko
University of Lethbridge
Kotaro Moriyama
Goethe University Frankfurt
National Astronomical Observatory of Japan
Vedant Dhruv
University of Illinois
Kazunori Akiyama
National Astronomical Observatory of Japan
Massachusetts Institute of Technology (MIT)
Harvard University
Antxon Alberdi
Spanish National Research Council (CSIC)
Walter Alef
Max Planck Society
Juan Carlos Algaba
University of Malaya
Richard Anantua
Harvard University
Rice University
Harvard-Smithsonian Center for Astrophysics
University of Texas
Keiichi Asada
Academia Sinica
Rebecca Azulay
Max Planck Society
Universitat de Valencia
Uwe Bach
Max Planck Society
David Ball
University of Arizona
Mislav Balokovic
Yale University
Bidisha Bandyopadhyay
University of Concepcion
John Barrett
Massachusetts Institute of Technology (MIT)
Michi Baubock
University of Illinois
Bradford A. Benson
Fermi National Accelerator Laboratory
University of Chicago
Dan Bintley
East Asian Observatory
James Clerk Maxwell Telescope
Lindy Blackburn
Harvard University
Harvard-Smithsonian Center for Astrophysics
Raymond Blundell
Harvard-Smithsonian Center for Astrophysics
Katherine L. Bouman
California Institute of Technology (Caltech)
Geoffrey C. Bower
James Clerk Maxwell Telescope
Academia Sinica
East Asian Observatory
University of Hawaii
Michael Bremer
Institut de Radioastronomie Millimétrique (IRAM)
Roger Brissenden
Harvard University
Harvard-Smithsonian Center for Astrophysics
Silke Britzen
Max Planck Society
Avery E. Broderick
University of Waterloo
Perimeter Institute for Theoretical Physics
Dominique Broguiere
Institut de Radioastronomie Millimétrique (IRAM)
Thomas Bronzwaer
Radboud University
Sandra Bustamante
University of Massachusetts
John E. Carlstrom
University of Chicago
Andrew Chael
Princeton University
Chi-kwan Chan
University of Arizona
Dominic O. Chang
Harvard-Smithsonian Center for Astrophysics
Harvard University
Koushik Chatterjee
Harvard-Smithsonian Center for Astrophysics
Harvard University
Shami Chatterjee
Cornell University
Ming-Tang Chen
Academia Sinica
Yongjun Chen
Chinese Academy of Sciences
Xiaopeng Cheng
Korea Astronomy and Space Science Institute
Pierre Christian
WattTime
Ilje Cho
Spanish National Research Council (CSIC)
Korea Astronomy and Space Science Institute
Yonsei University
Nicholas S. Conroy
Harvard-Smithsonian Center for Astrophysics
University of Illinois
Thomas M. Crawford
University of Chicago
Geoffrey B. Crew
Massachusetts Institute of Technology (MIT)
Alejandro Cruz-Osorio
Universidad Nacional Autónoma de México
Goethe University Frankfurt
Yuzhu Cui
Central China Normal University
Brandon Curd
University of Texas
Harvard University
Harvard-Smithsonian Center for Astrophysics
Rohan Dahale
Spanish National Research Council (CSIC)
Jordy Davelaar
National Aeronautics and Space Administration (NASA)
Princeton University
Mariafelicia De laurentis
University of Naples Federico II
National Institute for Nuclear Physics
Roger Deane
Rhodes University
University of Witwatersrand
University of Pretoria
Jessica Dempsey
James Clerk Maxwell Telescope
Netherlands Institute for Radio Astronomy (ASTRON)
East Asian Observatory
Gregory Desvignes
Paris Descartes University
Max Planck Society
Jason Dexter
University of Colorado
Indu K. Dihingia
Shanghai Jiao Tong University
Sheperd S. Doeleman
Harvard University
Harvard-Smithsonian Center for Astrophysics
Sergio A. Dzib
Max Planck Society
Ralph P. Eatough
Chinese Academy of Sciences
Max Planck Society
Razieh Emami
Harvard-Smithsonian Center for Astrophysics
Heino Falcke
Radboud University
Joseph Farah
Las Cumbres Observatory Global Telescope Network
University of California
Vincent L. Fish
Massachusetts Institute of Technology (MIT)
Edward Fomalont
National Radio Astronomy Observatory
H. Alyson Ford
University of Arizona
Marianna Foschi
Spanish National Research Council (CSIC)
Antonio Fuentes
Spanish National Research Council (CSIC)
Raquel Fraga-Encinas
Radboud University
William T. Freeman
Google Inc.
Massachusetts Institute of Technology (MIT)
Per Friberg
James Clerk Maxwell Telescope
East Asian Observatory
Christian M. Fromm
Max Planck Society
University of Würzburg
Goethe University Frankfurt
Peter Galison
Harvard University
Charles F. Gammie
University of Illinois
Roberto Garcia
Institut de Radioastronomie Millimétrique (IRAM)
Olivier Gentaz
Institut de Radioastronomie Millimétrique (IRAM)
Gertie Geertsema
Royal Netherlands Meteorological Institute
Boris Georgiev
University of Arizona
Roman Gold
Heidelberg University
University of Southern Denmark
Jose L. Gomez
Spanish National Research Council (CSIC)
Arturo I. Gomez-Ruiz
National Council for Science and Technology Mexico
National Institute of Astrophysics, Optics and Electronics
Minfeng Gu
Chinese Academy of Sciences
Mark Gurwell
Harvard-Smithsonian Center for Astrophysics
Kazuhiro Hada
Nagoya City University
National Astronomical Observatory of Japan
Daryl Haggard
McGill University
Ronald Hesper
University of Groningen
Dirk Heumann
University of Arizona
Luis C. Ho
Beijing University of Technology
Paul Ho
East Asian Observatory
Academia Sinica
James Clerk Maxwell Telescope
Mareki Honma
The Graduate University for Advanced Studies (SOKENDAI)
University of Tokyo
National Astronomical Observatory of Japan
Chih-Wei L. Huang
Academia Sinica
Lei Huang
Chinese Academy of Sciences
David H. Hughes
National Institute of Astrophysics, Optics and Electronics
Shiro Ikeda
The Institute of Statistical Mathematics
National Astronomical Observatory of Japan
University of Tokyo
The Graduate University for Advanced Studies (SOKENDAI)
C. M. Violette Impellizzeri
National Radio Astronomy Observatory
Leiden University
Makoto Inoue
Academia Sinica
Sara Issaoun
National Aeronautics and Space Administration (NASA)
Harvard-Smithsonian Center for Astrophysics
David J. James
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Buell T. Jannuzi
University of Arizona
Michael Janssen
Radboud University
Max Planck Society
Britton Jeter
Academia Sinica
Wu Jiang
Chinese Academy of Sciences
Alejandra Jimenez-Rosales
Radboud University
Michael D. Johnson
Harvard-Smithsonian Center for Astrophysics
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Adam C. Jones
University of Chicago
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Boston University
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University of Arizona
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University of Science and Technology (UST)
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Ramesh Karuppusamy
Max Planck Society
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University of Tokyo
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Harvard-Smithsonian Center for Astrophysics
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Joint Institute for VLBI in Europe (JIVE)
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Commonwealth Scientific and Industrial Research Organisation (CSIRO)
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Max Planck Society
Ulsan National Institute of Science and Technology (UNIST)
Jongsoo Kim
Korea Astronomy and Space Science Institute
Junhan Kim
Korea Advanced Institute of Science and Technology (KAIST)
Motoki Kino
Kogakuin University of Technology and Engineering
National Astronomical Observatory of Japan
Jun Yi Koay
Academia Sinica
Prashant Kocherlakota
Goethe University Frankfurt
Yutaro Kofuji
University of Tokyo
National Astronomical Observatory of Japan
Patrick M. Koch
Academia Sinica
Shoko Koyama
Academia Sinica
Niigata University
Carsten Kramer
Institut de Radioastronomie Millimétrique (IRAM)
Joana A. Kramer
Max Planck Society
Michael Kramer
Max Planck Society
Thomas P. Krichbaum
Max Planck Society
Cheng-Yu Kuo
Academia Sinica
National Sun Yat-Sen University
Noemi La Bella
Radboud University
Sang-Sung Lee
Korea Astronomy and Space Science Institute
Aviad Levis
California Institute of Technology (Caltech)
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Nanjing University
Rocco Lico
Italian ALMA Regional Centre
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Pontificia Universidad Católica de Valparaíso
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Max Planck Society
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Chinese Academy of Sciences
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Italian ALMA Regional Centre
Istituto nazionale di astrofisica (INAF)
Wen-Ping Lo
National Taiwan University
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Andrei P. Lobanov
Max Planck Society
Laurent Loinard
Harvard University
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Massachusetts Institute of Technology (MIT)
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University of Arizona
Ru-Sen Lu
Chinese Academy of Sciences
Max Planck Society
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Max Planck Society
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Chinese Academy of Sciences
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University of Amsterdam
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Boston University
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Massachusetts Institute of Technology (MIT)
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National Aeronautics and Space Administration (NASA)
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Goethe University Frankfurt
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University of Amsterdam
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Harvard University
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Institut de Radioastronomie Millimétrique (IRAM)
Aleksandar PopStefanija
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University of Amsterdam
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Ben Prather
University of Illinois
Giacomo Principe
National Institute for Nuclear Physics
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Georgia Institute of Technology
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National Taiwan Normal University
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Tokyo Institute of Technology
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Beijing University of Technology
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Chinese Academy of Sciences
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University of Science and Technology (UST)
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Chalmers, Space, Earth and Environment, Onsala Space Observatory
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Institute for Advanced Study
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Huazhong University of Science and Technology
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Doosoo Yoon
University of Amsterdam
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Radboud University
Ziri Younsi
University College London (UCL)
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Harvard-Smithsonian Center for Astrophysics
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Fudan University
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University of Science and Technology of China
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Michigan State University
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Chinese Academy of Sciences
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 708 A179Subject Categories (SSIF 2025)
Atom and Molecular Physics and Optics
Astronomy, Astrophysics, and Cosmology
Meteorology and Atmospheric Sciences
DOI
10.1051/0004-6361/202556759