The NANOGrav 15-year Gravitational-Wave Background Methods
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 GWB detection and parameter estimation perspectives. The tests presented here validate current analyses of PTA data.
Cite
@article{arxiv.2306.16223,
title = {The NANOGrav 15-year Gravitational-Wave Background Methods},
author = {Aaron D. Johnson and Patrick M. Meyers and Paul T. Baker and Neil J. Cornish and Jeffrey S. Hazboun and Tyson B. Littenberg and Joseph D. Romano and Stephen R. Taylor and Michele Vallisneri and Sarah J. Vigeland and Ken D. Olum and Xavier Siemens and Justin A. Ellis and Rutger van Haasteren and Sophie Hourihane and Gabriella Agazie and Akash Anumarlapudi and Anne M. Archibald and Zaven Arzoumanian and Laura Blecha and Adam Brazier and Paul R. Brook and Sarah Burke-Spolaor and Bence Bécsy and J. Andrew Casey-Clyde and Maria Charisi and Shami Chatterjee and Katerina Chatziioannou and Tyler Cohen and James M. Cordes and Fronefield Crawford and H. Thankful Cromartie and Kathryn Crowter and Megan E. DeCesar and Paul B. Demorest and Timothy Dolch and Brendan Drachler and Elizabeth C. Ferrara and William Fiore and Emmanuel Fonseca and Gabriel E. Freedman and Nate Garver-Daniels and Peter A. Gentile and Joseph Glaser and Deborah C. Good and Kayhan Gültekin and Ross J. Jennings and Megan L. Jones and Andrew R. Kaiser and David L. Kaplan and Luke Zoltan Kelley and Matthew Kerr and Joey S. Key and Nima Laal and Michael T. Lam and William G. Lamb and T. Joseph W. Lazio and Natalia Lewandowska and Tingting Liu and Duncan R. Lorimer and Ryan S. Lynch and Chung-Pei Ma and Dustin R. Madison and Alexander McEwen and James W. McKee and Maura A. McLaughlin and Natasha McMann and Bradley W. Meyers and Chiara M. F. Mingarelli and Andrea Mitridate and Cherry Ng and David J. Nice and Stella Koch Ocker and Timothy T. Pennucci and Benetge B. P. Perera and Nihan S. Pol and Henri A. Radovan and Scott M. Ransom and Paul S. Ray and Shashwat C. Sardesai and Carl Schmiedekamp and Ann Schmiedekamp and Kai Schmitz and Brent J. Shapiro-Albert and Joseph Simon and Magdalena S. Siwek and Ingrid H. Stairs and Daniel R. Stinebring and Kevin Stovall and Abhimanyu Susobhanan and Joseph K. Swiggum and Jacob E. Turner and Caner Unal and Haley M. Wahl and Caitlin A. Witt and Olivia Young},
journal= {arXiv preprint arXiv:2306.16223},
year = {2025}
}
Comments
30 pages, 10 figures, 1 table; Companion paper to "The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background"; For questions or comments, please email comments@nanograv.org; updated to journal version