NANOGrav 15-year gravitational-wave background methods

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, Michele; 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, Katerina; 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.; La...

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.

Citation

Johnson, A. D., Meyers, P. M., Baker, P. T., Cornish, N. J., Hazboun, J. S., Littenberg, T. B., …Young, O. (2024). NANOGrav 15-year gravitational-wave background methods. Physical Review D, 109(10), Article 103012. https://doi.org/10.1103/PhysRevD.109.103012

• Journal Article Type: Article
• Acceptance Date: Mar 21, 2024
• Online Publication Date: May 9, 2024
• Publication Date: May 15, 2024
• Deposit Date: May 23, 2024
• Publicly Available Date: May 28, 2024
• Journal: Physical Review D
• Print ISSN: 2470-0010
• Electronic ISSN: 2470-0029
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 109
• Issue: 10
• Article Number: 103012
• DOI: https://doi.org/10.1103/PhysRevD.109.103012
• Public URL: https://hull-repository.worktribe.com/output/4672922