Relativistic Jets and Winds in Radio-identified Supermassive Black Hole Binary Candidates
Creators
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1.
Kavli Institute for Particle Astrophysics and Cosmology
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2.
University of Crete
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3.
FORTH Institute of Astrophysics
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4.
University of Concepción
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5.
National Autonomous University of Mexico
- 6. JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309-0440, USA
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7.
National Institute of Standards and Technology
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8.
University of Colorado Boulder
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9.
California Institute of Technology
Abstract
Supermassive black hole binary systems (SMBHBs) are thought to emit the recently discovered nHz gravitational wave background; however, not a single individual nHz source has been confirmed to date. Long-term radio-monitoring at the Owens Valley Radio Observatory has revealed two potential SMBHB candidates: blazars PKS 2131-021 and PKS J0805-0111. These sources show periodic flux density variations across the electromagnetic spectrum, signaling the presence of a good clock. To explain the emission, we propose a generalizable jet model, where a mildly relativistic wind creates an outward-moving helical channel, along which the ultrarelativistic jet propagates. The observed flux variation from the jet is mostly due to aberration. The emission at a lower frequency arises at a larger radius, and its variation is consequently delayed, as observed. Our model reproduces the main observable features of both sources and can be applied to other sources as they are discovered. We make predictions for radio polarization, direct imaging, and emission line variation, which can be tested with forthcoming observations. Our results motivate future numerical simulations of jetted SMBHB systems and have implications for the fueling, structure, and evolution of blazar jets.
Copyright and License
© 2026. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
The authors thank Alisa Galishnikova, Martijn Oei, Timothy J. Pearson, Viraj Manwadkar, Jack Dinsmore, Roger W. Romani, Emanuele Sobacchi, Alexander Philippov, Lorenzo Sironi, and Paulo Coppi for useful discussions. The authors also thank the anonymous referee for useful feedback, which improved this manuscript. This work was supported in part by a grant from the Simons Foundation (00001470, R.B., A.G.S., N.G.). A.G.S. acknowledges the support of the Stanford University Physics Department Fellowship, the National Science Foundation Graduate Research Fellowship, and a Giddings Fellowship at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford. The work at the Owens Valley Radio Observatory is supported by NSF grants AST2407603 and AST2407604. We thank the California Institute of Technology and the Max Planck Institute for Radio Astronomy for supporting the OVRO 40 m program under extremely difficult circumstances over the last 8 yr in the absence of agency funding. Without this private support, these observations could not have been made. Prior to 2016, the OVRO program was supported by NASA grants NNG06GG1G, NNX08AW31G, NNX11A043G, and NNX13AQ89G from 2006 to 2016 and NSF grants AST-0808050 and AST-1109911 from 2008 to 2014.
Files
Sullivan_2026_ApJ_997_85.pdf
Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2510.02301 (arXiv)
Funding
- Simons Foundation
- 00001470
- Stanford University
- National Science Foundation
- AST2407603
- National Science Foundation
- AST2407604
- National Aeronautics and Space Administration
- NNG06GG1G
- National Aeronautics and Space Administration
- NNX08AW31G
- National Aeronautics and Space Administration
- NNX11A043G
- National Aeronautics and Space Administration
- NNX13AQ89G
- National Science Foundation
- AST-0808050
- National Science Foundation
- AST-1109911
Dates
- Submitted
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2025-10-02
- Accepted
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2025-11-25
- Available
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2026-01-15Published
Caltech Custom Metadata
- Caltech groups
- Astronomy Department , Owens Valley Radio Observatory , Division of Physics, Mathematics and Astronomy (PMA)
- Publication Status
- Published