Compelling Evidence for a Harmonic in the Light Curve of the Supermassive Black Hole Binary Candidate PKS J1309+1154
: Readhead, A. C. S.; Aller, M. F.; Sullivan, A. G.; Blandford, R. D.; Mróz, P.; De La Parra, P. V.; Molina, B.; Most, E. R.; Lister, M. L.; Synani, A.; Aller, H.; Begelman, M. C.; Ding, Y.; Graham, M. J.; Harrison, F.; Hovatta, T.; Liodakis, I.; Max-Moerbeck, W.; Pavlidou, V.; Pearson, T. J.; Ravi, V.; Reeves, R. A.; Surti, T.; Tassis, K.; Tremblay, S. E.; Zensus, J. A.
Publisher: Institute of Physics Publishing
: 2026
Astrophysical Journal Letters
: L39
: 996
: 2
: 2041-8205
: 2041-8213
DOI: https://doi.org/10.3847/2041-8213/ae2656
: https://iopscience.iop.org/article/10.3847/2041-8213/ae2656
: https://research.utu.fi/converis/portal/detail/Publication/515501428
We recently discovered a supermassive black hole binary (SMBHB) candidate, PKS J1309+1154, in the combined 46 yr University of Michigan Radio Astronomy Observatory (UMRAO) plus Owens Valley Radio Observatory (OVRO) blazar monitoring programs at 14.5/15 GHz. The light curve of PKS 1309+1154 exhibits a 17.9 yr periodicity. We also reported a hint of a first harmonic with a 9 yr periodicity in this object. Further analysis of the PKS J1309+1154 light curve provides compelling evidence that both the fundamental and the harmonic are real, confirming the existence of real periodicities in blazar light curves. This is the first case, to our knowledge, of watertight evidence for a fundamental periodicity and a harmonic periodicity in a blazar light curve. It makes PKS J1309+1154 a strong SMBHB candidate and thus the third such candidate to be revealed through long-term radio monitoring, the other two being PKS J0805–0111 and PKS 2131–021, both discovered through the OVRO 40 m Telescope monitoring program. It is argued that hundreds of SMBHB candidates will be discovered by the combination of the South Pole Telescope, the Vera Rubin Observatory, and the Simons Observatory. Coherent searches for gravitational waves from a network of SMBHB candidates, starting immediately, are strongly motivated.
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This work 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. Without this private support, this program would have ended in 2016. We also thank all the volunteers who have enabled this work to be carried out. 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. The UMRAO program received support from NSF grants AST-8021250, AST-8301234, AST-8501093, AST-8815678, AST-9120224, AST-9421979, AST-9900723, AST-0307629, AST-0607523, and earlier NSF awards, and from NASA grants NNX09AU16G, NNX10AP16G, NNX11AO13G, and NNX13AP18G. Additional funding for the operation of UMRAO was provided by the University of Michigan. W.M. acknowledges support from ANID project Basal FB210003. A.S. and R.B acknowledge support from a grant from the Simons Foundation (00001470, RB, AS). Y.D. and F.A.H. acknowledge support through NASA under contract No. NNG08FD60C. R.R. and B.M. and P.V.d.l.P. acknowledge support from ANID Basal AFB-170002, Núcleo Milenio TITANs (NCN2023_002), CATA BASAL FB210003, and UdeC-VRID 2025001479INV. T.H. acknowledges support from the Academy of Finland projects 317383, 320085, 345899, and 362571 and from the European Union ERC-2024-COG—PARTICLES—101169986. K.T. acknowledges the support from the TITAN ERA Chair project (contract no. 101086741) within the Horizon Europe Framework Program of the European Commission. This research is partially funded by the European Union. The views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. V.P. is supported by an ERC grant, mw-atlas project No. 101166905. I.L is funded by the European Union ERC-2022-STG—BOOTES—101076343.
