CaltechAUTHORS
Published February 10, 2026 | Version Published
Journal Article Open

The NANOGrav 15 yr Dataset: Targeted Searches for Supermassive Black Hole Binaries

Creators

  • 1. ROR icon West Virginia University
  • 2. ROR icon University of Wisconsin–Milwaukee
  • 3. ROR icon University of North Carolina at Chapel Hill
  • 4. ROR icon Newcastle University
  • 5. ROR icon Goddard Space Flight Center
  • 6. ROR icon Oregon State University
  • 7. ROR icon Widener University
  • 8. ROR icon University of Birmingham
  • 9. ROR icon University of Florida
  • 10. ROR icon Cornell University
  • 11. ROR icon University of Connecticut
  • 12. ROR icon Yale University
  • 13. ROR icon Washington State University
  • 14. ROR icon FORTH Institute of Astrophysics
  • 15. ROR icon New Mexico Institute of Mining and Technology
  • 16. ROR icon Montana State University
  • 17. ROR icon Franklin & Marshall College
  • 18. ROR icon National Academy of Sciences
  • 19. ROR icon United States Naval Research Laboratory
  • 20. ROR icon University of British Columbia
  • 21. ROR icon George Mason University
  • 22. ROR icon National Radio Astronomy Observatory
  • 23. ROR icon Columbia University
  • 24. ROR icon Hillsdale College
  • 25. ROR icon Eureka Scientific
  • 26. ROR icon Space Telescope Science Institute
  • 27. ROR icon Johns Hopkins University
  • 28. ROR icon University of Copenhagen
  • 29. ROR icon University of Maryland, College Park
  • 30. ROR icon University of California, Berkeley
  • 31. ROR icon Vanderbilt University
  • 32. ROR icon California Institute of Technology
  • 33. ROR icon University of Montana
  • 34. ROR icon University of Michigan–Ann Arbor
  • 35. NANOGrav Physics Frontiers Center Postdoctoral Fellow.
  • 36. Astrophysics Working Group, NANOGrav Collaboration, Berkeley, CA, 94720, USA
  • 37. University of Washington Bothell, 18115, Campus Way NE, Bothell, WA 98011, USA
  • 38. ROR icon Search for Extraterrestrial Intelligence
  • 39. ROR icon Rochester Institute of Technology
  • 40. ROR icon Jet Propulsion Lab
  • 41. ROR icon State University of New York at Oswego
  • 42. ROR icon Georgia State University
  • 43. ROR icon University of Toronto
  • 44. Deceased.
  • 45. Green Bank Observatory, P.O. Box 2, Green Bank, WV 24944, USA
  • 46. ROR icon Occidental College
  • 47. ROR icon Union College
  • 48. ROR icon Curtin University
  • 49. ROR icon International Centre for Radio Astronomy Research
  • 50. ROR icon Deutsches Elektronen-Synchrotron DESY
  • 51. ROR icon Harvard University
  • 52. ROR icon Lafayette College
  • 53. ROR icon Carnegie Observatories
  • 54. ROR icon Tufts University
  • 55. ROR icon Eötvös Loránd University
  • 56. ROR icon Arecibo Observatory
  • 57. ROR icon Texas Tech University
  • 58. ROR icon University of Puerto Rico System
  • 59. ROR icon Pennsylvania State University
  • 60. ROR icon University of Münster
  • 61. ROR icon University of Padua
  • 62. ROR icon INFN Sezione di Padova
  • 63. Giant Army, 915A 17th Ave, Seattle, WA 98122, USA
  • 64. ROR icon Oberlin College
  • 65. ROR icon Max Planck Institute for Gravitational Physics
  • 66. ROR icon Leibniz University Hannover
  • 67. ROR icon Wake Forest University

Abstract

We present the first targeted searches for continuous gravitational waves (CWs) from 114 active galactic nuclei that may host supermassive black hole binaries, using the NANOGrav 15 yr dataset. By incorporating electromagnetic priors on sky location, distance, redshift, and CW frequency, our strain and chirp-mass upper limits are typically improved by a factor of ∼2 (median 2.2) relative to all-sky limits at the same frequency. Bayesian comparisons against a model including only a Hellings–Downs-correlated background disfavors a CW signal for all targets, with a mean Bayes factor of 0.73 ± 0.32. Two targets have Bayes factors slightly above unity, but coherence tests, random-targeting experiments, and a conservative accounting of the 114-target trials factor all indicate that they are consistent with noise. We use these two candidates as worked examples to illustrate an end-to-end targeted CW search analysis and a suite of follow-up tests that future promising candidates would need to pass. We find that the electromagnetic interpretations of both candidates are ambiguous, and we update the constraints on a putative binary in 3C 66B, ruling out part of its previously allowed parameter space. Ultimately, our results demonstrate the current sensitivity of targeted pulsar timing array searches for CWs and define a road map for future multimessenger CW detections.

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

C.M.F.M. thanks F. van den Bosch, B. Farr, J. Greene, K. Grunthal, D. Holz, N. Navon, V. Ozoliņš, T. A. Prince, C. M. Urry, and A. Vecchio. The work contained herein has been carried out by the NANOGrav collaboration, which receives support from the National Science Foundation (NSF) Physics Frontier Center award numbers 1430284 and 2020265, the Gordon and Betty Moore Foundation, NSF AccelNet award number 2114721, an NSERC Discovery Grant, and CIFAR. The Arecibo Observatory is a facility of the NSF operated under cooperative agreement (AST-1744119) by the University of Central Florida (UCF) in alliance with Universidad Ana G. Mendez (UAGM) and Yang Enterprises (YEI), Inc. The Green Bank Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. L.B. acknowledges support from the National Science Foundation under award AST-2307171, the National Aeronautics and Space Administration under award 80NSSC22K0808, and the Research Corporation for Science Advancement under Cottrell Scholar Award No. 27553. P.R.B. is supported by the Science and Technology Facilities Council, grant No. ST/W000946/1. P.N. acknowledges support from the Gordon and Betty Moore Foundation and the John Templeton Foundation that fund the Black Hole Initiative (BHI) at Harvard University, where she serves as one of the PIs. S.B.S. gratefully acknowledges the support of a Sloan Fellowship and the support of the NSF under award #2408649. The work of R.B., N.L., X.S., J.T., and D.W. is partly supported by the George and Hannah Bolinger Memorial Fund in the College of Science at Oregon State University. M.C., P.P., and S.R.T. acknowledge support from NSF AST-2007993. M.C. was supported by the Vanderbilt Initiative in Data-Intensive Astrophysics (VIDA) Fellowship. M.C. acknowledges support by the European Union (ERC, MMMonsters, 101117624). Support for this work was provided by the NSF through the Grote Reber Fellowship Program administered by Associated Universities, Inc./National Radio Astronomy Observatory. Pulsar research at UBC is supported by an NSERC Discovery Grant and by CIFAR. K.C. is supported by a UBC Four Year Fellowship (6456). M.E.D. acknowledges support from the Naval Research Laboratory by NASA under contract S-15633Y. T.D. and M.T.L. received support from NSF Astronomy and Astrophysics Grant (AAG) award number 2009468 during this work. E.C.F. is supported by NASA under award number 80GSFC24M0006. G.E.F., S.C.S., and S.J.V. are supported by NSF award PHY-2011772. K.A.G. and S.R.T. acknowledge support from an NSF CAREER award #2146016. M.J.G. is supported by NSF #2108402. A.D.J. and M.V. acknowledge support from the Caltech and Jet Propulsion Laboratory President’s and Director’s Research and Development Fund. A.D.J. acknowledges support from the Sloan Foundation. N.L. acknowledges the support from the Larry W. Martin and Joyce B. O’Neill Endowed Fellowship in the College of Science at Oregon State University. 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 (80NM0018D0004). D.R.L. and M.A.M. are supported by NSF #1458952. M.A.M. is supported by NSF #2009425. C.M.F.M. was supported in part by the National Science Foundation under grants No. NSF PHY-1748958, AST-2106552, and NASA LPS 80NSSC24K0440. The research of C.M.F.M. was also supported in part by grant NSF PHY-2309135 to the Kavli Institute for Theoretical Physics (KITP). A.M. is supported by the Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy—EXC 2121 Quantum Universe—390833306. The Dunlap Institute is funded by an endowment established by the David Dunlap family and the University of Toronto. K.D.O. was supported in part by NSF grant No. 2207267. T.T.P. acknowledges support from the Extragalactic Astrophysics Research Group at Eötvös Loránd University, funded by the Eötvös Loránd Research Network (ELKH), which was used during the development of this research. H.A.R. is supported by NSF Partnerships for Research and Education in Physics (PREP) award No. 2216793. S.M.R. and I.H.S. are CIFAR Fellows. Portions of this work performed at NRL were supported by ONR 6.1 basic research funding. J.D.R. also acknowledges support from start-up funds at Texas Tech University. J.S. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2202388 and acknowledges previous support from the NSF under award 1847938. C.A.W. acknowledges support from CIERA, the Adler Planetarium, and the Brinson Foundation through a CIERA–Adler postdoctoral fellowship. O.Y. is supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE-2139292. E.E. was funded in part by a NASA-CT Space Grant, PTE Federal Award No: 80NSSC25M7127. Y.C. was supported by a STARS II Fellowship and a NASA-CT Space Grant, PTE Federal Award No: 80NSSC20M0129.

Contributions

The authors are listed alphabetically to acknowledge that a long-term effort like NANOGrav, spanning over a decade, is fundamentally a collective enterprise. All contributors participated in collaborative activities that enabled the results presented in this work, and each reviewed the manuscript—including its text and figures—before submission. Additional specific contributions to this Letter are as follows.

C.M.F.M. conceived the project, led the searches, and coordinated the writing of this Letter. The analysis was performed by F.H., B.L., N.A., L.W., J.A.C.C., R.S., C.M.F.M., and S.B.S., who produced the figures and tables. F.H. and B.L. developed new and independent targeted search pipelines to run with enterprise, with the help of R.S. C.A.W. originally developed the targeted search methodologies and enterprise-based code adaptations for CW analyses under the supervision of S.B.S., S.T., and S.V. and has provided training on and documentation of these techniques for the collaboration. Those developments and trainings have informed the broader CW efforts within NANOGrav, including the work presented here. Additional specific contributions to the original enterprise-based targeted search code for the NANOGrav 11 yr dataset can be found in Z. Arzoumanian et al. (2020). N.A. and L.W. carried out the QuickCW searches with help from B.B., S.B.S., and L.D. The Letter was written by C.M.F.M, F.H., B.L, F.S., and B.B., with contributions from N.A., S.B.S., and Q.Z. The analysis of the GWB anisotropy was derived by F.S. The dropout searches and incoherent and coherent searches were carried out by B.B. Posterior reweighting analyses to account for HD correlations were carried out by B.L. for enterprise searches and N.A for QuickCW searches. The extension of the CRTS light curves for SDSS J1536+0441 and J0729+4008 was carried out by M.G. and P.C. The discussion about EM counterparts for SDSS J1536+0441 and J0729+4008 was written by C.M.F.M, F.H., T.J.L., M.G., P.C., S.B.S., J.R., P.N., M.C., D.D., T.B., and K.G. Additional comments during review were contributed by J.R., D.D., T.J.L., S.C., L.B., C.A.W., S.V., and S.R.T.

Data Availability

A repository for reproducing the results of the enterprise searches can be found on Zenodo via the dataset “The NANOGrav 15 yr Data Set: Targeted Searches for Supermassive Black Hole Binaries,” available at 10.5281/zenodo.17289574. This repository contains posterior samples from Markov Chain Monte Carlo chains, HD weight factors, EM target priors, as well as Jupyter notebooks and Python scripts for carrying out analyses.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2508.16534 (arXiv)
Is supplemented by
Dataset: 10.5281/zenodo.17289574 (DOI)

Funding

National Science Foundation
1430284
National Science Foundation
2020265
Gordon and Betty Moore Foundation
National Science Foundation
2114721
Natural Sciences and Engineering Research Council
Canadian Institute for Advanced Research
National Science Foundation
AST-1744119
National Science Foundation
AST-2307171
National Aeronautics and Space Administration
80NSSC22K0808
Research Corporation for Science Advancement
Cottrell Scholar Award 27553
Science and Technology Facilities Council
ST/W000946/1
John Templeton Foundation
Alfred P. Sloan Foundation
National Science Foundation
2408649
Oregon State University
College of Science -
National Science Foundation
AST-2007993
European Union
101117624
University of British Columbia
6456
National Aeronautics and Space Administration
S-15633Y
National Science Foundation
2009468
National Aeronautics and Space Administration
80GSFC24M0006
National Science Foundation
PHY-2011772
National Science Foundation
2146016
National Science Foundation
2108402
California Institute of Technology
Jet Propulsion Laboratory
National Aeronautics and Space Administration
80NM0018D0004
National Science Foundation
1458952
National Science Foundation
2009425
National Science Foundation
PHY-1748958
National Science Foundation
AST-2106552
National Aeronautics and Space Administration
80NSSC24K0440
National Science Foundation
PHY-2309135
Deutsche Forschungsgemeinschaft
EXC 2121 390833306
National Science Foundation
2207267
Eötvös Loránd University
National Science Foundation
2216793
Office of Naval Research
Texas Tech University
National Science Foundation
AST-2202388
National Science Foundation
1847938
Northwestern University
CIERA -
Adler Planetarium
Brinson Foundation
National Science Foundation
DGE-2139292
National Aeronautics and Space Administration
80NSSC25M7127
National Aeronautics and Space Administration
80NSSC20M0129

Dates

Submitted
2025-08-22
Accepted
2026-01-07
Available
2026-02-05
Published

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Caltech groups
Division of Physics, Mathematics and Astronomy (PMA) , Physics Department
Publication Status
Published