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Published December 10, 2023 | Version Published
Journal Article Open

How to Detect an Astrophysical Nanohertz Gravitational Wave Background

Creators

  • 1. ROR icon Oregon State University
  • 2. ROR icon Montana State University
  • 3. ROR icon California Institute of Technology
  • 4. ROR icon University of California, Berkeley
  • 5. ROR icon University of Wisconsin–Milwaukee
  • 6. ROR icon Newcastle University
  • 7. ROR icon Goddard Space Flight Center
  • 8. ROR icon Widener University
  • 9. ROR icon University of Florida
  • 10. ROR icon Cornell University
  • 11. ROR icon University of Birmingham
  • 12. ROR icon West Virginia University
  • 13. ROR icon University of Connecticut
  • 14. ROR icon Vanderbilt University
  • 15. ROR icon New Mexico Institute of Mining and Technology
  • 16. ROR icon Franklin & Marshall College
  • 17. ROR icon University of British Columbia
  • 18. ROR icon United States Naval Research Laboratory
  • 19. ROR icon National Radio Astronomy Observatory
  • 20. ROR icon Hillsdale College
  • 21. ROR icon Eureka Scientific
  • 22. ROR icon University of Maryland, College Park
  • 23. ROR icon University of Michigan–Ann Arbor
  • 24. ROR icon University of Washington
  • 25. ROR icon Search for Extraterrestrial Intelligence
  • 26. ROR icon Rochester Institute of Technology
  • 27. ROR icon Jet Propulsion Lab
  • 28. ROR icon State University of New York at Oswego
  • 29. ROR icon Marshall Space Flight Center
  • 30. ROR icon University of Toronto
  • 31. ROR icon University of the Pacific
  • 32. ROR icon University of Hull
  • 33. ROR icon International Centre for Radio Astronomy Research
  • 34. ROR icon Yale University
  • 35. ROR icon Deutsches Elektronen-Synchrotron DESY
  • 36. ROR icon Lafayette College
  • 37. ROR icon Carnegie Observatories
  • 38. ROR icon Tufts University
  • 39. ROR icon Eötvös Loránd University
  • 40. ROR icon Arecibo Observatory
  • 41. ROR icon University of Puerto Rico System
  • 42. ROR icon Texas Tech University
  • 43. ROR icon Pennsylvania State University
  • 44. ROR icon University of Münster
  • 45. ROR icon University of Colorado Boulder
  • 46. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 47. ROR icon Oberlin College
  • 48. ROR icon Middle East Technical University
  • 49. ROR icon Ben-Gurion University of the Negev
  • 50. ROR icon Feza Gürsey Institute
  • 51. ROR icon Max Planck Institute for Gravitational Physics
  • 52. ROR icon Northwestern University
  • 53. ROR icon Adler Planetarium

Abstract

Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source of this background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for this background and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, and most often, (iii) a power-law spectrum. However, a stochastic background from a finite collection of binaries does not exactly satisfy any of these assumptions. To understand the effect of these assumptions, we test standard analysis techniques on a large collection of realistic simulated data sets. The data-set length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15 yr data set. Simulated signals from millions of binaries drawn from models based on the Illustris cosmological hydrodynamical simulation were added to the data. We find that the standard statistical methods perform remarkably well on these simulated data sets, even though their fundamental assumptions are not strictly met. They are able to achieve a confident detection of the background. However, even for a fixed set of astrophysical parameters, different realizations of the universe result in a large variance in the significance and recovered parameters of the background. We also find that the presence of loud individual binaries can bias the spectral recovery of the background if we do not account for them.

Copyright and License

© 2023. 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

We appreciate the support of the NSF Physics Frontiers Center Award PFC-1430284 and the NSF Physics Frontiers Center Award PFC-2020265. L.B. acknowledges support from the National Science Foundation under award AST-1909933 and from 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. S.B. gratefully acknowledges the support of a Sloan Fellowship and the support of NSF under award #1815664. M.C. and S.R.T. acknowledge support from NSF AST-2007993. M.C. and N.S.P. were supported by the Vanderbilt Initiative in Data Intensive Astrophysics (VIDA) Fellowship. K.Ch., A.D.J., and M.V. acknowledge support from the Caltech and Jet Propulsion Laboratory President's and Director's Research and Development Fund. K.Ch. and A.D.J. acknowledge support from the Sloan Foundation. Support for this work was provided by the NSF through the Grote Reber Fellowship Program administered by Associated Universities, Inc./National Radio Astronomy Observatory. Support for H.T.C. is provided by NASA through the NASA Hubble Fellowship Program grant #HST-HF2-51453.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Pulsar research at UBC is supported by an NSERC Discovery Grant and by CIFAR. K.Cr. 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. are supported by an NSF Astronomy and Astrophysics Grant (AAG) award number 2009468. E.C.F. is supported by NASA under award number 80GSFC21M0002. G.E.F., S.C.S., and S.J.V. are supported by NSF award PHY-2011772. The Flatiron Institute is supported by the Simons Foundation. S.H. is supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE-1745301. The work of N.La. and X.S. is partly supported by the George and Hannah Bolinger Memorial Fund in the College of Science at Oregon State University. N.La. acknowledges the support from 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 grant Nos. NSF PHY-1748958 and AST-2106552. A.Mi. 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. 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 from Texas Tech University. J.S. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2202388, and acknowledges previous support by the NSF under award 1847938. S.R.T. acknowledges support from an NSF CAREER award #2146016. C.U. acknowledges support from BGU (Kreitman fellowship), and the Council for Higher Education and Israel Academy of Sciences and Humanities (Excellence fellowship). 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.

Software References

enterprise (Ellis et al. 2019), enterprise_extensions (Taylor et al. 2021), QuickCW (Bécsy et al. 2023), corner (Foreman-Mackey 2016), libstempo (Vallisneri 2020), tempo (Nice et al. 2015), tempo2 (Hobbs et al. 2006), PINT (Luo et al. 2019), matplotlib (Hunter 2007), astropy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018)

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Additional details

Identifiers

ISSN
1538-4357

Funding

National Science Foundation
PHY-1430284
National Science Foundation
PHY-2020265
National Science Foundation
AST-1909933
Research Corporation for Science Advancement
Cottrell Scholar 27553
Science and Technology Facilities Council
ST/W000946/1
Alfred P. Sloan Foundation
ST/W000946/1
National Science Foundation
AST-1815664
National Science Foundation
AST-2007993
Vanderbilt University
California Institute of Technology
President's and Director's Research and Development Fund
National Radio Astronomy Observatory
Grote Reber Fellowship
National Aeronautics and Space Administration
NASA Hubble Fellowship HST-HF2-51453.001
National Aeronautics and Space Administration
NAS5-26555
Natural Sciences and Engineering Research Council
Canadian Institute for Advanced Research
University of British Columbia
6456
United States Naval Research Laboratory
S-15633Y
National Science Foundation
AST-2009468
National Aeronautics and Space Administration
80GSFC21M0002
National Science Foundation
PHY-2011772
Simons Foundation
National Science Foundation
NSF Graduate Research Fellowship DGE-1745301
Oregon State University
National Aeronautics and Space Administration
80NM0018D0004`
National Science Foundation
OIA-1458952
National Science Foundation
AST-2009425
National Science Foundation
PHY-1748958
National Science Foundation
AST-2106552
Deutsche Forschungsgemeinschaft
390833306
University of Toronto
National Science Foundation
PHY-2207267
Eötvös Loránd University
Office of Naval Research
6.1
Texas Tech University
National Science Foundation
NSF Astronomy and Astrophysics Fellowship AST-2202388
National Science Foundation
AST-1847938
National Science Foundation
PHY-2146016
Ben-Gurion University of the Negev
Council for Higher Education
Israel Academy of Sciences and Humanities
Northwestern University
Center for Interdisciplinary Exploration and Research in Astrophysics
Adler Planetarium
Brinson Foundation
National Science Foundation
NSF Graduate Research Fellowship DGE-2139292

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Caltech groups
Astronomy Department, TAPIR, Walter Burke Institute for Theoretical Physics