A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
PKS 2131-021-Discovery of Strong Coherent Sinusoidal Variations from Radio to Optical Frequencies: Compelling Evidence for a Blazar Supermassive Black Hole Binary
Tekijät: Kiehlmann, S.; de la Parra, P. V.; Sullivan, A. G.; Synani, A.; Liodakis, I.; Mroz, P.; Naess, S. K.; Readhead, A. C. S.; Begelman, M. C.; Blandford, R. D.; Chatziioannou, K.; Ding, Y.; Graham, M. J.; Harrison, F.; Homan, D. C.; Hovatta, T.; Kulkarni, S. R.; Lister, M. L.; Maiolino, R.; Max-Moerbeck, W.; Molina, B.; O'Dea, C. P.; Pavlidou, V.; Pearson, T. J.; Aller, M. F.; Lawrence, C. R.; Lazio, T. J. W.; O'Neill, S.; Prince, T. A.; Ravi, V.; Reeves, R. A.; Tassis, K.; Vallisneri, M.; Zensus, J. A.
Kustantaja: IOP Publishing Ltd
Kustannuspaikka: BRISTOL
Julkaisuvuosi: 2025
Journal: Astrophysical Journal
Tietokannassa oleva lehden nimi: ASTROPHYSICAL JOURNAL
Lehden akronyymi: ASTROPHYS J
Artikkelin numero: 59
Vuosikerta: 985
Numero: 1
Sivujen määrä: 22
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/adc567
Verkko-osoite: https://iopscience.iop.org/article/10.3847/1538-4357/adc567
Rinnakkaistallenteen osoite: https://research.utu.fi/converis/portal/detail/Publication/492254569
Haystack and Owens Valley Radio Observatory observations recently revealed strong, intermittent, sinusoidal total flux-density variations that maintained their coherence between 1975 and 2021 in the blazar PKS 2131-021 (z = 1.283). This was interpreted as possible evidence of a supermassive black hole binary (SMBHB). Extended observations through 2023 show a coherence over 47.9 yr, with an observed period P-15 GHz = (1739.8 +/- 17.4) days. We reject, with p-value = 2.09 x 10(-7), the hypothesis that the variations are due to random fluctuations in the red noise tail of the power spectral density. There is clearly a physical phenomenon in PKS 2131-021 producing coherent sinusoidal flux-density variations. We find the coherent sinusoidal intensity variations extend from below 2.7 GHz to optical frequencies, from which we derive an observed period P-optical = (1764 +/- 36) days. Across this broad frequency range, there is a smoothly varying monotonic phase shift in the sinusoidal variations with frequency. Hints of periodic variations are also observed at gamma-ray energies. The importance of well-vetted SMBHB candidates to searches for gravitational waves is pointed out. We estimate the fraction of blazars that are SMBHB candidates to be >1 in 100. Thus, monitoring programs covering tens of thousands of blazars could discover hundreds of SMBHB candidates.
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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 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. We thank Adam Hincks for useful discussions. 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. S.K. and K.T. acknowledge support from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation program under grant agreement No. 771282. I.L and S.K. were funded by the European Union ERC-2022-STG—BOOTES—101076343. 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. W.M. acknowledges support from ANID project Basal FB210003. A.S. and R.B acknowledge support by a grant from the Simons Foundation (00001470,RB,AS). R.R. and B.M. and P.V.d.l.P. acknowledge support from ANID Basal AFB-170002, from Núcleo Milenio TITANs (NCN2023_002), and CATA BASAL FB210003. P.V.d.l.P. also acknowledges support by the National Agency for Research and Development (ANID)/Scholarship Program/Doctorado Nacional/2023–21232103. C.O. acknowledges support from the Natural Sciences and Engineering Research Council (NSERC) of Canada. T.H. acknowledges support from the Academy of Finland projects 317383, 320085, 322535, and 345899. The NANOGrav collaboration receives support from National Science Foundation (NSF) Physics Frontiers Center award Nos. 1430284 and 2020265. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00001.CAL. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSTC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.
