NANOGrav 15-year gravitational-wave background methods

Creators: Johnson, Aaron D.; Meyers, Patrick M.; Baker, Paul T.; Cornish, Neil J.; Hazboun, Jeffrey S.; Littenberg, Tyson B.; Romano, Joseph D.; Taylor, Stephen R.; Vallisneri, Michele¹; Vigeland, Sarah J.; Olum, Ken D.; Siemens, Xavier; Ellis, Justin A.; van Haasteren, Rutger; Hourihane, Sophie; Agazie, Gabriella; Anumarlapudi, Akash; Archibald, Anne M.; Arzoumanian, Zaven; Blecha, Laura; Brazier, Adam; Brook, Paul R.; Burke-Spolaor, Sarah; Bécsy, Bence; Casey-Clyde, J. Andrew; Charisi, Maria; Chatterjee, Shami; Chatziioannou, Katerina¹; Cohen, Tyler; Cordes, James M.; Crawford, Fronefield; Cromartie, H. Thankful; Crowter, Kathryn; DeCesar, Megan E.; Demorest, Paul B.; Dolch, Timothy; Drachler, Brendan; Ferrara, Elizabeth C.; Fiore, William; Fonseca, Emmanuel; Freedman, Gabriel E.; Garver-Daniels, Nate; Gentile, Peter A.; Glaser, Joseph; Good, Deborah C.; Gültekin, Kayhan; Jennings, Ross J.; Jones, Megan L.; Kaiser, Andrew R.; Kaplan, David L.; Kelley, Luke Zoltan; Kerr, Matthew; Key, Joey S.; Laal, Nima; Lam, Michael T.; Lamb, William G.; Lazio, T. Joseph W.; Lewandowska, Natalia; Liu, Tingting; Lorimer, Duncan R.; Luo, Jing; Lynch, Ryan S.; Ma, Chung-Pei; Madison, Dustin R.; McEwen, Alexander; McKee, James W.; McLaughlin, Maura A.; McMann, Natasha; Meyers, Bradley W.; Mingarelli, Chiara M. F.; Mitridate, Andrea; Ng, Cherry; Nice, David J.; Ocker, Stella Koch; Pennucci, Timothy T.; Perera, Benetge B. P.; Pol, Nihan S.; Radovan, Henri A.; Ransom, Scott M.; Ray, Paul S.; Sardesai, Shashwat C.; Schmiedekamp, Carl; Schmiedekamp, Ann; Schmitz, Kai; Shapiro-Albert, Brent J.; Simon, Joseph; Siwek, Magdalena S.; Stairs, Ingrid H.; Stinebring, Daniel R.; Stovall, Kevin; Susobhanan, Abhimanyu; Swiggum, Joseph K.; Turner, Jacob E.; Unal, Caner; Wahl, Haley M.; Witt, Caitlin A.; Young, Olivia; NANOGrav Collaboration

1. California Institute of Technology

Abstract

Pulsar timing arrays (PTAs) use an array of millisecond pulsars to search for gravitational waves in the nanohertz regime in pulse time of arrival data. This paper presents rigorous tests of PTA methods, examining their consistency across the relevant parameter space. We discuss updates to the 15-year isotropic gravitational-wave background analyses and their corresponding code representations. Descriptions of the internal structure of the flagship algorithms enterprise and ptmcmcsampler are given to facilitate understanding of the PTA likelihood structure, how models are built, and what methods are currently used in sampling the high-dimensional PTA parameter space. We introduce a novel version of the PTA likelihood that uses a two-step marginalization procedure that performs much faster in gravitational wave searches, reducing the required resources facilitating the computation of Bayes factors via thermodynamic integration and sampling a large number of realizations for computing Bayesian false-alarm probabilities. We perform stringent tests of consistency and correctness of the Bayesian and frequentist analysis methods. For the Bayesian analysis, we test prior recovery, simulation recovery, and Bayes factors. For the frequentist analysis, we test that the optimal statistic, when modified to account for a non-negligible gravitational-wave background, accurately recovers the amplitude of the background. We also summarize recent advances and tests performed on the optimal statistic in the literature from both gravitational wave background detection and parameter estimation perspectives. The tests presented here validate current analyses of PTA data.

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Acknowledgement

The NANOGrav project receives support from National Science Foundation (NSF) Physics Frontiers Center Award No. 1430284. A. D. J., K. C., and M. V. acknowledge support from the Caltech and Jet Propulsion Laboratory President’s and Director’s Research and Development Fund. A. D. J. and K. C. acknowledge support from the Sloan Foundation. S. H. is supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1745301. L. B. acknowledges support from the National Science Foundation under Award No. 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 No. 1815664. M. C. and S. R. T. acknowledge support from Grant No. NSF AST-2007993. M. C. and N. S. P. were supported by the Vanderbilt Initiative in Data Intensive Astrophysics (VIDA) Fellowship. 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 No. 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 No. NAS5-26555. M. E. D. acknowledges support from the Naval Research Laboratory by NASA under Contract No. S-15633Y. T. D. and M. T. L. are supported by an NSF Astronomy and Astrophysics Grant (AAG) Award No. 2009468. E. C. F. is supported by NASA under Award No. 80GSFC21M0002. G. E. F., S. C. S., and S. J. V. are supported by NSF Award No. PHY-2011772. The Flatiron Institute is supported by the Simons Foundation. The work of N. L. and X. S. is partly supported by the George and Hannah Bolinger Memorial Fund in the College of Science at Oregon State University. N. L. 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 (Grant No. 80NM0018D0004). M. A. M. is supported by NSF Grants No. 1458952 and 2009425. C. M. F. M. was supported in part by the National Science Foundation under Grants No. NSF PHY-1748958 and No. AST-2106552. A. Mi. is supported by the Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy—EXC 2121 Quantum Universe—Grant No. 390833306. 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 N. R. L. 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 No. AST-2202388, and acknowledges previous support by the NSF under Award No. 1847938. Pulsar research at U. B. C. is supported by an NSERC Discovery Grant and by CIFAR. S. R. T. acknowledges support from an NSF CAREER Award No. 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. J. A. C. C. was supported in part by NASA CT Space Grant PTE Federal Award No. 80NSSC20M0129, and also supported in part by the National Science Foundation’s NANOGrav Physics Frontier Center, Award No. 2020265. H. T. C. has NASA Hubble Fellowship: Einstein Postdoctoral Fellow. R. J. J. and J. K. S. is NANOGrav Physics Frontiers Center Postdoctoral Fellow.

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