@ARTICLE{2026A&A...708A.179A,
author = {{Albentosa-Ruiz}, Ezequiel and {Washington}, Jasmin E. and {Marchili}, Nicola and {Mart{\'\i}-Vidal}, Iv{\'a}n and {Goddi}, Ciriaco and {Wielgus}, Maciek and {Mus}, Alejandro and {Ricarte}, Angelo and {Marrone}, Daniel P. and {Salas}, Le{\'o}n D.~S. and {Iwata}, Yuhei and {Carlos}, Douglas F. and {Tetarenko}, Alexandra J. and {Moriyama}, Kotaro and {Dhruv}, Vedant and {Akiyama}, Kazunori and {Alberdi}, Antxon and {Alef}, Walter and {Carlos Algaba}, Juan and {Anantua}, Richard and {Asada}, Keiichi and {Azulay}, Rebecca and {Bach}, Uwe and {Baczko}, Anne-Kathrin and {Ball}, David and {Balokovi{\'c}}, Mislav and {Bandyopadhyay}, Bidisha and {Barrett}, John and {Baub{\"o}ck}, Michi and {Benson}, Bradford A. and {Bintley}, Dan and {Blackburn}, Lindy and {Blundell}, Raymond and {Bouman}, Katherine L. and {Bower}, Geoffrey C. and {Bremer}, Michael and {Brissenden}, Roger and {Britzen}, Silke and {Broderick}, Avery E. and {Broguiere}, Dominique and {Bronzwaer}, Thomas and {Bustamante}, Sandra and {Carlstrom}, John E. and {Chael}, Andrew and {Chan}, Chi-kwan and {Chang}, Dominic O. and {Chatterjee}, Koushik and {Chatterjee}, Shami and {Chen}, Ming-Tang and {Chen}, Yongjun and {Cheng}, Xiaopeng and {Christian}, Pierre and {Cho}, Ilje and {Conroy}, Nicholas S. and {Conway}, John E. and {Crawford}, Thomas M. and {Crew}, Geoffrey B. and {Cruz-Osorio}, Alejandro and {Cui}, Yuzhu and {Curd}, Brandon and {Dahale}, Rohan and {Davelaar}, Jordy and {De Laurentis}, Mariafelicia and {Deane}, Roger and {Dempsey}, Jessica and {Desvignes}, Gregory and {Dexter}, Jason and {Dihingia}, Indu K. and {Doeleman}, Sheperd S. and {Dzib}, Sergio A. and {Eatough}, Ralph P. and {Emami}, Razieh and {Falcke}, Heino and {Farah}, Joseph and {Fish}, Vincent L. and {Fomalont}, Edward and {Alyson Ford}, H. and {Foschi}, Marianna and {Fuentes}, Antonio and {Fraga-Encinas}, Raquel and {Freeman}, William T. and {Friberg}, Per and {Fromm}, Christian M. and {Galison}, Peter and {Gammie}, Charles F. and {Garc{\'\i}a}, Roberto and {Gentaz}, Olivier and {Geertsema}, Gertie and {Georgiev}, Boris and {Gold}, Roman and {G{\'o}mez}, Jos{\'e} L. and {G{\'o}mez-Ruiz}, Arturo I. and {Gu}, Minfeng and {Gurwell}, Mark and {Hada}, Kazuhiro and {Haggard}, Daryl and {Hesper}, Ronald and {Heumann}, Dirk and {Ho}, Luis C. and {Ho}, Paul and {Honma}, Mareki and {Huang}, Chih-Wei L. and {Huang}, Lei and {Hughes}, David H. and {Ikeda}, Shiro and {Violette Impellizzeri}, C.~M. and {Inoue}, Makoto and {Issaoun}, Sara and {James}, David J. and {Jannuzi}, Buell T. and {Janssen}, Michael and {Jeter}, Britton and {Jiang}, Wu and {Jim{\'e}nez-Rosales}, Alejandra and {Johnson}, Michael D. and {Jones}, Adam C. and {Jorstad}, Svetlana and {Joshi}, Abhishek V. and {Jung}, Taehyun and {Karuppusamy}, Ramesh and {Kawashima}, Tomohisa and {Keating}, Garrett K. and {Kettenis}, Mark and {Kim}, Dong-Jin and {Kim}, Jae-Young and {Kim}, Jongsoo and {Kim}, Junhan and {Kino}, Motoki and {Yi Koay}, Jun and {Kocherlakota}, Prashant and {Kofuji}, Yutaro and {Koch}, Patrick M. and {Koyama}, Shoko and {Kramer}, Carsten and {Kramer}, Joana A. and {Kramer}, Michael and {Krichbaum}, Thomas P. and {Kuo}, Cheng-Yu and {La Bella}, Noemi and {Lee}, Sang-Sung and {Levis}, Aviad and {Li}, Zhiyuan and {Lico}, Rocco and {Lindahl}, Greg and {Lindqvist}, Michael and {Lisakov}, Mikhail and {Liu}, Jun and {Liu}, Kuo and {Liuzzo}, Elisabetta and {Lo}, Wen-Ping and {Lobanov}, Andrei P. and {Loinard}, Laurent and {Lonsdale}, Colin J. and {Lowitz}, Amy E. and {Lu}, Ru-Sen and {MacDonald}, Nicholas R. and {Mao}, Jirong and {Markoff}, Sera and {Marscher}, Alan P. and {Matsushita}, Satoki and {Matthews}, Lynn D. and {Medeiros}, Lia and {Menten}, Karl M. and {Mizuno}, Izumi and {Mizuno}, Yosuke and {Montgomery}, Joshua and {Moran}, James M. and {Moscibrodzka}, Monika and {Mulaudzi}, Wanga and {M{\"u}ller}, Hendrik and {M{\"u}ller}, Cornelia and {Musoke}, Gibwa and {Myserlis}, Ioannis and {Nagai}, Hiroshi and {Nagar}, Neil M. and {Nair}, Dhanya G. and {Nakamura}, Masanori and {Narayanan}, Gopal and {Natarajan}, Iniyan and {Nathanail}, Antonios and {Navarro Fuentes}, Santiago and {Neilsen}, Joey and {Ni}, Chunchong and {Nowak}, Michael A. and {Oh}, Junghwan and {Okino}, Hiroki and {Olivares S{\'a}nchez}, H{\'e}ctor Ra{\'u}l and {Oyama}, Tomoaki and {{\"O}zel}, Feryal and {Palumbo}, Daniel C.~M. and {Paraschos}, Georgios Filippos and {Park}, Jongho and {Parsons}, Harriet and {Patel}, Nimesh and {Pen}, Ue-Li and {Pesce}, Dominic W. and {Pi{\'e}tu}, Vincent and {PopStefanija}, Aleksandar and {Porth}, Oliver and {Prather}, Ben},
title = "{Full-polarization millimeter wavelength variability of Sagittarius A$^{*}$ during the 2018 EHT campaign}",
journal = {\aap},
keywords = {black hole physics, techniques: interferometric, techniques: polarimetric, Galaxy: center, Astrophysics of Galaxies, High Energy Astrophysical Phenomena},
year = 2026,
month = apr,
volume = {708},
eid = {A179},
pages = {A179},
abstract = "{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 ({\ensuremath{\sigma}}/{\ensuremath{\mu}} < 10\%), but
significantly higher variability in linear and circular
polarization ({\ensuremath{\sim}}30\% and
{\ensuremath{\sim}}50\%, respectively). A time-series analysis
reveals red-noise variability, with power spectral densities
between {\ensuremath{-}}2 and {\ensuremath{-}}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.}",
doi = {10.1051/0004-6361/202556759},
archivePrefix = {arXiv},
eprint = {2604.10287},
primaryClass = {astro-ph.GA},
adsurl = {https://ui.adsabs.harvard.edu/abs/2026A&A...708A.179A},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
