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The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background

Agazie, Gabriella; Anumarlapudi, Akash; Archibald, Anne M.; Arzoumanian, Zaven; Baier, Jeremy; Baker, Paul T.; Bécsy, Bence; Blecha, Laura; Brazier, Adam; Brook, Paul R.; Burke-Spolaor, Sarah; Burnette, Rand; Case, Robin; Casey-Clyde, J. Andrew; Charisi, Maria; Chatterjee, Shami; Cohen, Tyler; Cordes, James M.; Cornish, Neil J.; Crawford, Fronefield; Cromartie, H. Thankful; Crowter, Kathryn; DeCesar, Megan E.; DeGan, Dallas; 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; Hazboun, Jeffrey S.; Jennings, Ross J.; Johnson, Aaron D.; 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, Dusti...

Authors

Gabriella Agazie

Akash Anumarlapudi

Anne M. Archibald

Zaven Arzoumanian

Jeremy Baier

Paul T. Baker

Bence Bécsy

Laura Blecha

Adam Brazier

Paul R. Brook

Sarah Burke-Spolaor

Rand Burnette

Robin Case

J. Andrew Casey-Clyde

Maria Charisi

Shami Chatterjee

Tyler Cohen

James M. Cordes

Neil J. Cornish

Fronefield Crawford

H. Thankful Cromartie

Kathryn Crowter

Megan E. DeCesar

Dallas DeGan

Paul B. Demorest

Timothy Dolch

Brendan Drachler

Elizabeth C. Ferrara

William Fiore

Emmanuel Fonseca

Gabriel E. Freedman

Nate Garver-Daniels

Peter A. Gentile

Joseph Glaser

Deborah C. Good

Kayhan Gültekin

Jeffrey S. Hazboun

Ross J. Jennings

Aaron D. Johnson

Megan L. Jones

Andrew R. Kaiser

David L. Kaplan

Luke Zoltan Kelley

Matthew Kerr

Joey S. Key

Nima Laal

Michael T. Lam

William G. Lamb

T. Joseph W. Lazio

Natalia Lewandowska

Tingting Liu

Duncan R. Lorimer

Jing Luo

Ryan S. Lynch

Chung Pei Ma

Dustin R. Madison

Alexander McEwen

James W. McKee

Maura A. McLaughlin

Natasha McMann

Bradley W. 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

Nihan S. Pol

Henri A. Radovan

Scott M. Ransom

Paul S. Ray

Joseph D. Romano

Alexander Saffer

Shashwat C. Sardesai

Ann Schmiedekamp

Carl Schmiedekamp

Kai Schmitz

Brent J. Shapiro-Albert

Xavier Siemens

Joseph Simon

Magdalena S. Siwek

Ingrid H. Stairs

Daniel R. Stinebring

Kevin Stovall

Jerry P. Sun

Abhimanyu Susobhanan

Joseph K. Swiggum

Jacob A. Taylor

Stephen R. Taylor

Jacob E. Turner

Caner Unal

Michele Vallisneri

Sarah J. Vigeland

Haley M. Wahl

Caitlin A. Witt

Olivia Young

The NANOGrav Collaboration



Abstract

Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes, which produce different interpulsar correlations. In this work, we search the NANOGrav 15 yr data set for evidence of a gravitational-wave background with quadrupolar HD and scalar-transverse (ST) correlations. We find that HD correlations are the best fit to the data and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors ∼2 when comparing HD to ST correlations, and ∼1 for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis.

Citation

Agazie, G., Anumarlapudi, A., Archibald, A. M., Arzoumanian, Z., Baier, J., Baker, P. T., Bécsy, B., Blecha, L., Brazier, A., Brook, P. R., Burke-Spolaor, S., Burnette, R., Case, R., Casey-Clyde, J. A., Charisi, M., Chatterjee, S., Cohen, T., Cordes, J. M., Cornish, N. J., Crawford, F., …The NANOGrav Collaboration. (2024). The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background. Astrophysical journal. Letters, 964(1), L14. https://doi.org/10.3847/2041-8213/ad2a51

Journal Article Type Article
Acceptance Date Feb 16, 2024
Online Publication Date Mar 18, 2024
Publication Date Mar 20, 2024
Deposit Date Mar 25, 2024
Publicly Available Date Mar 25, 2024
Journal Astrophysical Journal Letters
Print ISSN 2041-8205
Electronic ISSN 2041-8213
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 964
Issue 1
Pages L14
DOI https://doi.org/10.3847/2041-8213/ad2a51
Keywords Space and Planetary Science; Astronomy and Astrophysics
Public URL https://hull-repository.worktribe.com/output/4611097

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Copyright Statement
© 2024. The Author(s).
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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