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The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

Agazie, Gabriella; Anumarlapudi, Akash; Archibald, Anne M.; Arzoumanian, Zaven; Baker, Paul T.; Bécsy, Bence; Blecha, Laura; Brazier, Adam; Brook, Paul R.; Burke-Spolaor, Sarah; Burnette, Rand; Case, Robin; Charisi, Maria; Chatterjee, Shami; Chatziioannou, Katerina; Cheeseboro, Belinda D.; Chen, Siyuan; Cohen, Tyler; Cordes, James M.; Cornish, Neil J.; Crawford, Fronefield; Cromartie, H. Thankful; Crowter, Kathryn; Cutler, Curt J.; DeCesar, Megan E.; DeGan, Dallas; Demorest, Paul B.; Deng, Heling; Dolch, Timothy; Drachler, Brendan; Ellis, Justin A.; Ferrara, Elizabeth C.; Fiore, William; Fonseca, Emmanuel; Freedman, Gabriel E.; Garver-Daniels, Nate; Gentile, Peter A.; Gersbach, Kyle A.; Glaser, Joseph; Good, Deborah C.; Gültekin, Kayhan; Hazboun, Jeffrey S.; Hourihane, Sophie; Islo, Kristina; Jennings, Ross J.; Johnson, Aaron D.; Jones, Megan L.; Kaiser, Andrew R.; Kaplan, David L.; Kelley, Luke Zoltan; Kerr, Matthew; Key, Joey S.; Klein, Tonia C.; Laal, Nima; Lam, Michael T.; Lamb, Wi...


Gabriella Agazie

Akash Anumarlapudi

Anne M. Archibald

Zaven Arzoumanian

Paul T. Baker

Bence Bécsy

Laura Blecha

Adam Brazier

Paul R. Brook

Sarah Burke-Spolaor

Rand Burnette

Robin Case

Maria Charisi

Shami Chatterjee

Katerina Chatziioannou

Belinda D. Cheeseboro

Siyuan Chen

Tyler Cohen

James M. Cordes

Neil J. Cornish

Fronefield Crawford

H. Thankful Cromartie

Kathryn Crowter

Curt J. Cutler

Megan E. DeCesar

Dallas DeGan

Paul B. Demorest

Heling Deng

Timothy Dolch

Brendan Drachler

Justin A. Ellis

Elizabeth C. Ferrara

William Fiore

Emmanuel Fonseca

Gabriel E. Freedman

Nate Garver-Daniels

Peter A. Gentile

Kyle A. Gersbach

Joseph Glaser

Deborah C. Good

Kayhan Gültekin

Jeffrey S. Hazboun

Sophie Hourihane

Kristina Islo

Ross J. Jennings

Aaron D. Johnson

Megan L. Jones

Andrew R. Kaiser

David L. Kaplan

Luke Zoltan Kelley

Matthew Kerr

Joey S. Key

Tonia C. Klein

Nima Laal

Michael T. Lam

William G. Lamb

T. Joseph W. Lazio

Natalia Lewandowska

Tyson B. Littenberg

Tingting Liu

Andrea Lommen

Duncan R. Lorimer

Jing Luo

Ryan S. Lynch

Chung Pei Ma

Dustin R. Madison

Margaret A. Mattson

Alexander McEwen

Maura A. McLaughlin

Natasha McMann

Bradley W. Meyers

Patrick M. Meyers

Chiara M.F. Mingarelli

Andrea Mitridate

Priyamvada Natarajan

Cherry Ng

David J. Nice

Stella Koch Ocker

Ken D. Olum

Timothy T. Pennucci

Benetge B.P. Perera

Polina Petrov

Nihan S. Pol

Henri A. Radovan

Scott M. Ransom

Paul S. Ray

Joseph D. Romano

Shashwat C. Sardesai

Ann Schmiedekamp

Carl Schmiedekamp

Kai Schmitz

Levi Schult

Brent J. Shapiro-Albert

Xavier Siemens

Joseph Simon

Magdalena S. Siwek

Ingrid H. Stairs

Daniel R. Stinebring

Kevin Stovall


We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings-Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 1014, and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200-1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10−3 (≈3σ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10−5 to 1.9 × 10−4 (≈3.5σ-4σ). Assuming a fiducial f −2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is 2.4 − 0.6 + 0.7 × 10 − 15 (median + 90% credible interval) at a reference frequency of 1 yr−1. The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings-Downs correlations points to the gravitational-wave origin of this signal.


Agazie, G., Anumarlapudi, A., Archibald, A. M., Arzoumanian, Z., Baker, P. T., Bécsy, B., …Stovall, K. (2023). The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background. Astrophysical journal. Letters, 951(1), Article L8.

Journal Article Type Article
Acceptance Date Jun 1, 2023
Online Publication Date Jun 29, 2023
Publication Date Jul 1, 2023
Deposit Date Jul 14, 2023
Publicly Available Date Jul 24, 2023
Journal Astrophysical Journal Letters
Print ISSN 2041-8205
Electronic ISSN 2041-8213
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 951
Issue 1
Article Number L8
Public URL


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Copyright Statement
© 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.

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