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Cited by 112Astrophysical Phenomena and ObservationsPulsars and Gravitational Waves ResearchRadio Astronomy Observations and Technology

Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign

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Wielgus, Maciek, Marchili, Nicola, Martí-Vidal, Iván, Keating, Garrett K., Ramakrishnan, Venkatessh, Tiede, Paul, Fomalont, Ed, Issaoun, Sara +259 more·2025·The Astrophysical Journal Letters
DOI 10.3847/2041-8213/ac6428
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Abstract

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.

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  • After several hours, the variable components of the image structure in Sgr A* are expected to be uncorrelated.

    “After several hours, the variable components of the image structure in Sgr A * are expected to be uncorrelated”

    From First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass (2022) · cites this paper as Wielgus et al. 2022

    Section 4.4 (p. 18) reports that autocorrelation in Sgr A*’s millimeter light curves decreases on a roughly one-hour timescale, consistent with weaker correlations after several hours. But this measures flux-density variability, not the correlation of variable image-structure components; the Summary and Discussion (p. 24) also says the correlation timescale remains poorly constrained. (LLM, conf=0.84)

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  • The variability behavior is consistent with theoretical expectations from GRMHD simulations and empirical expectations from the Sgr A* light curve, both of which imply that the variable elements of Sgr A* emission should be uncorrelated beyond a timescale of a few hours.

    “Furthermore, the variability behavior is consistent with theoretical expectations from GRMHD simulations and empirical expectations from the Sgr A * light curve, both of which imply that the variable elements of the Sgr A * emission should be uncorrelated beyond a timescale of a few hours”

    From First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass (2022) · cites this paper as Wielgus et al. 2022

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  • Variability was observed in the light curve of Sgr A* during the 2017 EHT campaign on timescales from 1 minute to several hours.

    “Such variability was also observed in the light curve of Sgr A * during the 2017 EHT campaign on timescales from 1 minute to several hours”

    From First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass (2022) · cites this paper as Wielgus et al. 2022

  • Observations of total flux variability in Sgr A* find a red-noise spectrum extending to timescales of several hours and flattening on longer timescales.

    “Observations of the total fl ux variability in Sgr A * corroborate this expectation, fi nding a red-noise spectrum extending to timescales of several hours and fl attening on longer timescales”

    From First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass (2022) · cites this paper as Wielgus et al. 2022

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Research works printed but not linked: 2

  1. Rasmussen, C. E., & Williams, C. K. I. 2006, Gaussian Processes for Machine Learning ( Cambridge, MA: MIT Press )
  2. Ricarte, A., Gammie, C., Narayan, R., & Prather, B. S. 2022, arXiv:2202. 02408

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Authors
Wielgus, M., Marchili, N., Martí-Vidal, I., Keating, G. K., Ramakrishnan, V., Tiede, P., Fomalont, E., Issaoun, S., Neilsen, J., Nowak, M. A., Blackburn, L., Gammie, C. F., Goddi, C., Haggard, D., Lee, D., Moscibrodzka, M., Tetarenko, A. J., Bower, G. C., Chan, C.-K., Chatterjee, K., Chesler, P. M., Dexter, J., Doeleman, S. S., Georgiev, B., Gurwell, M., Johnson, M. D., Marrone, D. P., Mus, A., Psaltis, D., Ripperda, B., Witzel, G., Akiyama, K., Alberdi, A., Alef, W., Carlos Algaba, J., Anantua, R., Asada, K., Azulay, R., Bach, U., Baczko, A.-K., Ball, D., Baloković, M., Barrett, J., Bauböck, M., Benson, B. A., Bintley, D., Blundell, R., Boland, W., Bouman, K. L., Boyce, H., Bremer, M., Brinkerink, C. D., Brissenden, R., Britzen, S., Broderick, A. E., Broguiere, D., Bronzwaer, T., Bustamante, S., Byun, D.-Y., Carlstrom, J. E., Ceccobello, C., Chael, A., Chatterjee, S., Chen, M.-T., Chen 陈, Y. 永., Cho, I., Christian, P., Conroy, N. S., Conway, J. E., Cordes, J. M., Crawford, T. M., Crew, G. B., Cruz-Osorio, A., Cui, Y., Davelaar, J., De Laurentis, M., Deane, R., Dempsey, J., Desvignes, G., Dhruv, V., Dzib, S. A., Eatough, R. P., Emami, R., Falcke, H., Farah, J., Fish, V. L., Alyson Ford, H., Fraga-Encinas, R., Freeman, W. T., Friberg, P., Fromm, C. M., Fuentes, A., Galison, P., García, R., Gentaz, O., Gold, R., Gómez-Ruiz, A. I., Gómez, J. L., Gu 顾, M. 敏., Hada, K., Haworth, K., Hecht, M. H., Hesper, R., Ho 何, L. C. 子., Ho, P., Honma, M., Huang, C.-W. L., Huang 黄, L. 磊., Hughes, D. H., Ikeda, S., Violette Impellizzeri, C. M., Inoue, M., James, D. J., Jannuzi, B. T., Janssen, M., Jeter, B., Jiang 江, W. 悟., Jiménez-Rosales, A., Jorstad, S., Joshi, A. V., Jung, T., Karami, M., Karuppusamy, R., Kawashima, T., Kettenis, M., Kim, D.-J., Kim, J.-Y., Kim, J., Kim, J., Kino, M., Yi Koay, J., Kocherlakota, P., Kofuji, Y., Koch, P. M., Koyama, S., Kramer, C., Kramer, M., Krichbaum, T. P., Kuo, C.-Y., La Bella, N., Lauer, T. R., Lee, S.-S., Kin Leung, P., Levis, A., Li 李, Z. 志., Lico, R., Lindahl, G., Lindqvist, M., Lisakov, M., Liu 刘, J. 俊., Liu, K., Liuzzo, E., Lo, W.-P., Lobanov, A. P., Loinard, L., Lonsdale, C., Lu 路, R.-S. 如., Mao 毛, J. 基., Markoff, S., Marscher, A. P., Matsushita, S., Matthews, L. D., Medeiros, L., Menten, K. M., Michalik, D., Mizuno, I., Mizuno, Y., Moran, J. M., Moriyama, K., Müller, C., Musoke, G., Myserlis, I., Nadolski, A., Nagai, H., Nagar, N. M., Nakamura, M., Narayan, R., Narayanan, G., Natarajan, I., Nathanail, A., Navarro Fuentes, S., Neri, R., Ni, C., Noutsos, A., Oh, J., Okino, H., Olivares, H., Ortiz-León, G. N., Oyama, T., Özel, F., Palumbo, D. C. M., Filippos Paraschos, G., Park, J., Parsons, H., Patel, N., Pen, U.-L., Pesce, D. W., Piétu, V., Plambeck, R., PopStefanija, A., Porth, O., Pötzl, F. M., Prather, B., Preciado-López, J. A., Pu, H.-Y., Rao, R., Rawlings, M. G., Raymond, A. W., Rezzolla, L., Ricarte, A., Roelofs, F., Rogers, A., Ros, E., Romero-Canizales, C., Roshanineshat, A., Rottmann, H., Roy, A. L., Ruiz, I., Ruszczyk, C., Rygl, K. L. J., Sánchez, S., Sánchez-Argüelles, D., Sánchez-Portal, M., Sasada, M., Satapathy, K., Savolainen, T., Peter Schloerb, F., Schuster, K.-F., Shao, L., Shen 沈, Z. 志., Small, D., Won Sohn, B., SooHoo, J., Souccar, K., Sun 孙, H. 赫., Tazaki, F., Tilanus, R. P. J., Titus, M., Torne, P., Traianou, E., Trent, T., Trippe, S., van Bemmel, I., Jan van Langevelde, H., van Rossum, D. R., Vos, J., Wagner, J., Ward-Thompson, D., Wardle, J., Weintroub, J., Wex, N., Wharton, R., Wiik, K., Wondrak, M. F., Wong, G. N., Wu 吴, Q. 庆., Yamaguchi, P., Yoon, D., Young, A., Young, K., Younsi, Z., Yuan 袁, F. 峰., Yuan 袁, Y.-F. 业., Anton Zensus, J., Zhang, S., Zhao, G.-Y., & Zhao, S.-S.
Affiliations
  • Max Planck Institute for Radio Astronomy (DE)
  • Istituto di Radioastronomia di Bologna (IT)
  • Universitat de València (ES)
  • Center for Astrophysics Harvard & Smithsonian (US)
  • University of Turku (FI)
  • Harvard University (US)
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  • Instituto de Astrofísica de Andalucía (ES)
  • Institute of Astronomy and Astrophysics, Academia Sinica (TW)
  • Yale University (US)
  • Massachusetts Institute of Technology (US)
  • Fermi National Accelerator Laboratory (US)
  • East Asian Observatory (US)
  • Nederlandse Onderzoekschool Voor Astronomie (NL)
  • California Institute of Technology (US)
  • Institut de Radioastronomie Millimétrique (FR)
  • Radboud University Nijmegen (NL)
  • University of Massachusetts Amherst (US)
  • Korea Astronomy and Space Science Institute (KR)
  • University of Chicago (US)
  • Chalmers University of Technology (SE)
  • Cornell University (US)
  • Fairfield University (US)
  • Goethe University Frankfurt (DE)
  • Shanghai Jiao Tong University (CN)
  • University of the Witwatersrand (ZA)
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  • Chinese Academy of Sciences (CN)
  • Las Cumbres Observatory Global Telescope Network (US)
  • Google (United States) (US)
  • National Institute of Astrophysics, Optics and Electronics (MX)
  • The Graduate University for Advanced Studies, SOKENDAI (JP)
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  • Kavli Institute for the Physics and Mathematics of the Universe (JP)
  • Boston University (US)
  • Institute for Cosmic Ray Research (JP)
  • Joint Institute for VLBI ERIC (NL)
  • Kogakuin University (JP)
  • National Astronomical Observatory of Japan (JP)
  • Universidad Nacional Autónoma de México (MX)
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  • Perimeter Institute (CA)
  • Hiroshima University (JP)
  • Peking University (CN)
  • Leiden University (NL)
  • Seoul National University (KR)
  • University of Lancashire (GB)
  • Brandeis University (US)
  • Bard College (US)
Corresponding author
  • Wielgus, Maciek
  • Keating, Garrett K.
ORCID
Venue
The Astrophysical Journal Letters
Publisher
American Astronomical Society
Published
2022-05-12
Volume
930
Issue
2
Pages
L19
ISSN
  • 2041-8205 (ISSN-L)
  • 2041-8213
DOI
10.3847/2041-8213/ac6428
OpenAlex
W4280611431
Cited by
112
References
117
Citations by year
2026: 14 · 2025: 22 · 2024: 35 · 2023: 20 · 2022: 21
FWCI
9.67
Type
journal article
Language
en
Open access
Licence
Locations
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Funders
  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek (639.043.513)
  • Science and Technology Facilities Council (ST/V000268/1)
  • Japan Society for the Promotion of Science (18K13594)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Pulsars and Gravitational Waves Research
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Radio Astronomy Observations and Technology
Keywords
Sgr A*, Event Horizon Telescope, Galactic Center, X-ray flares, spectral energy distribution, optical depth, Gaussian process modeling, compact radio sources

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