Spatially resolved polarization swings in the supermassive binary black hole candidate OJ 287 with first Event Horizon Telescope observations

We present the first Event Horizon Telescope 1.3 mm observations of the supermassive binary black hole candidate OJ 287. The observations achieved an unprecedented angular resolution of 18 μas and reveal significant structural and polarization variability over just five days, marking the shortest timescale on which such changes have been directly imaged in this source. The inner jet exhibits a twisted ridgeline structure, with features displaying apparent superluminal motions up to about 22 c. The linear polarization maps reveal three main polarized features whose electric-vector position angles (EVPAs) change substantially over the time span of our observations, including a component with a radial polarization consistent with being produced by a recollimation shock. Most notably, we directly resolved two innermost jet components whose EVPAs rotate in opposite directions. The faster component, moving at 2.4 ± 0.9 μas/day (17.4 ± 6.5 c), exhibits counterclockwise EVPA swings of roughly 3.7° per day, while the slower component, with a proper motion of 1.4 ± 0.3 μas/day (10.2 ± 2.2 c), rotates clockwise at approximately 2.5° per day. Previous studies inferred helical magnetic fields in AGN jets from time-resolved or integrated polarization variability but lacked the angular resolution to directly image this effect. Our results provide spatially resolved evidence that a helical magnetic field threads the jet’s collimation and acceleration zone, ruling out models based on the superposition of unresolved components. Our analysis suggests that propagating shocks interact with a Kelvin–Helmholtz plasma instability, illuminating different phases of the helical magnetic field and producing the observed polarization spatial and temporal variability. Moreover, our model naturally accounts for the more rapid polarization rotation observed in the faster moving component. Our model predicts even more rapid swings in polarization, which could be tested with future observations featuring a more densely sampled time coverage.

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Publication Details

Journal
Springer Link (Chiba Institute of Technology)
Published
2026-01-08
DOI
https://doi.org/10.1051/0004-6361/202555831/pdf
Primary Topic
Astrophysical Phenomena and Observations
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article
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article

Spatially resolved polarization swings in the supermassive binary black hole candidate OJ 287 with first Event Horizon Telescope observations

Chi‐kwan Chan, S. Britzen, Ezequiel Albentosa-Ruíz, S. Ikeda et al.
Springer Link (Chiba Institute of Technology)
Astrophysical Phenomena and Observations
article

Spatially resolved polarization swings in the supermassive binary black hole candidate OJ 287 with first Event Horizon Telescope observations

Chi‐kwan Chan, S. Britzen, Ezequiel Albentosa-Ruíz, S. Ikeda, Kazunori Akiyama, Andrew Chael, Boris Georgiev, S. Komossa, M. A. Janssen, Chen Mingtang, Indu K. Dihingia, Hendrik Müller, M. Perucho, Jan Röder, Sunil Chandra, Chi Kwan Chan, Rocco Lico, Uwe Bach, Jun Yi Koay, 江悟, 路如森, J. Davelaar, Antxon Alberdi, Keiichi Asada, Ilje Cho, Junhan Kim, Richard Anantua, Daniel P. Marrone, Teresa Toscano, Thomas Bronzwaer, Sandra Bustamante, Thomas P. Krichbaum, Michi Bauböck, Achamveedu Gopakumar, Raymond Blundell, Noemi La Bella, Douglas F. Carlos, Efthalia Traianou, Maciek Wielgus, José L. Gómez, John E. Carlstrom, John E. Conway, Katherine L. Bouman, Geoffrey C. Bower, William T. Freeman, Saurabh, Dominique Broguiere, Michael D. Johnson, Nicholas S. Conroy, Roman Gold, F. Peter Schloerb, Rebecca Azulay, Anne-Kathrin Baczko, Kotaro Moriyama, Sheperd S. Doeleman, Michael Kramer, David H. Hughes, Svetlana Jorstad, Dan Bintley, Ramprasad Rao, Amy E. Lowitz, Andrei P. Lobanov, Gabriele Bruni, Juan Carlos Algaba, Bidisha Bandyopadhyay, David Ball, Walter Alef, Nicholas R. MacDonald, Antonio Fuentes, Rohan Dahale, Dominic W. Pesce, Yuri Y. Kovalev, H. Alyson Ford, John Barrett, José M. Martí, Sara Issaoun, Hiroshi Nagai, Helge Rottmann, Guang-Yao Zhao, Koushik Chatterjee, Christian M. Fromm, Shami Chatterjee, Mauri J. Valtonen, David J. James, Thomas M. Crawford, Xiaopeng Cheng, Roger Brissenden, Bradford A. Benson, Avery E. Broderick, Daryl Haggard, David H. Hughes, Lia Medeiros, Remo P. J. Tilanus, Andrei P. Lobanov, Ramesh Karuppusamy, Huib Jan van Langevelde
article en

Abstract

We present the first Event Horizon Telescope 1.3 mm observations of the supermassive binary black hole candidate OJ 287. The observations achieved an unprecedented angular resolution of 18 μas and reveal significant structural and polarization variability over just five days, marking the shortest timescale on which such changes have been directly imaged in this source. The inner jet exhibits a twisted ridgeline structure, with features displaying apparent superluminal motions up to about 22 c. The linear polarization maps reveal three main polarized features whose electric-vector position angles (EVPAs) change substantially over the time span of our observations, including a component with a radial polarization consistent with being produced by a recollimation shock. Most notably, we directly resolved two innermost jet components whose EVPAs rotate in opposite directions. The faster component, moving at 2.4 ± 0.9 μas/day (17.4 ± 6.5 c), exhibits counterclockwise EVPA swings of roughly 3.7° per day, while the slower component, with a proper motion of 1.4 ± 0.3 μas/day (10.2 ± 2.2 c), rotates clockwise at approximately 2.5° per day. Previous studies inferred helical magnetic fields in AGN jets from time-resolved or integrated polarization variability but lacked the angular resolution to directly image this effect. Our results provide spatially resolved evidence that a helical magnetic field threads the jet’s collimation and acceleration zone, ruling out models based on the superposition of unresolved components. Our analysis suggests that propagating shocks interact with a Kelvin–Helmholtz plasma instability, illuminating different phases of the helical magnetic field and producing the observed polarization spatial and temporal variability. Moreover, our model naturally accounts for the more rapid polarization rotation observed in the faster moving component. Our model predicts even more rapid swings in polarization, which could be tested with future observations featuring a more densely sampled time coverage.

Springer Link (Chiba Institute of Technology)
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Astrophysical Phenomena and Observations
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