The NANOGrav 15 yr Dataset: Improved Timing Precision with Very Long Baseline Interferometry Astrometric Priors

Abstract Accurate pulsar astrometric estimates are essential to almost all high-precision pulsar timing experiments. Traditional pulsar timing techniques refine these estimates by including them as free parameters when fitting a model to observed pulse time-of-arrival measurements. However, reliable submilliarcsecond astrometric estimations require years of observations. Even then, power from red noise can be inadvertently absorbed into astrometric parameter fits. This effect biases the resulting estimates and reduces the sensitivity to red noise processes, including gravitational waves (GWs). In this work, we seek to mitigate these shortcomings by using pulsar astrometric estimates derived from very long baseline interferometry (VLBI) as priors for the timing fit. First, we used VLBI and timing astrometric estimates of 18 millisecond pulsars to calibrate a rotation between the reference frames used in timing and VLBI, with a precision of ∼0.7 mas. Through this frame tie, we combined timing- and VLBI-based probabilities to obtain a maximum-posterior astrometric solution. We found offsets between our results and the timing-based astrometric solutions, which, if real, would lead to the absorption of spectral power at the frequencies of interest for single-source GW searches. However, we do not find significant power absorption due to astrometric fitting at the low-frequency domain of the GW background.

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Publication Details

Journal
The Astrophysical Journal
Published
2026-03-02
DOI
https://doi.org/10.3847/1538-4357/ae39c9
Primary Topic
Pulsars and Gravitational Waves Research
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article
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article

The NANOGrav 15 yr Dataset: Improved Timing Precision with Very Long Baseline Interferometry Astrometric Priors

Carl Schmiedekamp, P. C. Ray, William Fiore, Abhimanyu Susobhanan et al.
The Astrophysical Journal
Pulsars and Gravitational Waves Research
article

The NANOGrav 15 yr Dataset: Improved Timing Precision with Very Long Baseline Interferometry Astrometric Priors

Carl Schmiedekamp, P. C. Ray, William Fiore, Abhimanyu Susobhanan, Peter A. Gentile, Kathryn Crowter, Ann Schmiedekamp, M. S. de Biasi, Joseph K. Swiggum, Kevin Stovall, Timothy Dolch, Nihan S. Pol, Scott Ransom, Paul T. Baker, Henri A. Radovan, Michael T. Lam, Ryan S. Lynch, Sofia V. Sosa Fiscella, Haley M. Wahl, Natasha McMann, Joseph Glaser, Jeffrey S. Hazboun, David J. Nice, H. Thankful Cromartie, Paul R. Brook, Gabriella Agazie, Jing Luo, Bradley W. Meyers, Anne M. Archibald, Deborah C. Good, Megan E. DeCesar, Brent J. Shapiro-Albert, David L. Kaplan, Emmanuel Fonseca, Paul B. Demorest, Benetge B. P. Perera, Ingrid H. Stairs, Duncan R. Lorimer, Ross J. Jennings, Zaven Arzoumanian, Gabriel E. Freedman, Maura A. McLaughlin, Akash Anumarlapudi, Cherry Ng, Elizabeth C. Ferrara, Alexander McEwen, Nate Garver-Daniels, Megan L. Jones, Timothy T. Pennucci, Matthew Kerr
article en

Abstract

Abstract Accurate pulsar astrometric estimates are essential to almost all high-precision pulsar timing experiments. Traditional pulsar timing techniques refine these estimates by including them as free parameters when fitting a model to observed pulse time-of-arrival measurements. However, reliable submilliarcsecond astrometric estimations require years of observations. Even then, power from red noise can be inadvertently absorbed into astrometric parameter fits. This effect biases the resulting estimates and reduces the sensitivity to red noise processes, including gravitational waves (GWs). In this work, we seek to mitigate these shortcomings by using pulsar astrometric estimates derived from very long baseline interferometry (VLBI) as priors for the timing fit. First, we used VLBI and timing astrometric estimates of 18 millisecond pulsars to calibrate a rotation between the reference frames used in timing and VLBI, with a precision of ∼0.7 mas. Through this frame tie, we combined timing- and VLBI-based probabilities to obtain a maximum-posterior astrometric solution. We found offsets between our results and the timing-based astrometric solutions, which, if real, would lead to the absorption of spectral power at the frequencies of interest for single-source GW searches. However, we do not find significant power absorption due to astrometric fitting at the low-frequency domain of the GW background.

The Astrophysical JournalVol. 999(2)
Eötvös Loránd University (HU), University of North Carolina at Chapel Hill (US), West Virginia University (US), Texas Tech University (US), United States Naval Research Laboratory (US), Goddard Space Flight Center (US), Pennsylvania State University (US), Oregon State University (US), National Academy of Sciences (US), Widener University (US), University of British Columbia (CA), Rochester Institute of Technology (US), George Mason University (US), Lafayette College (US), University of Toronto (CA), National Academies of Sciences, Engineering, and Medicine (US), Vanderbilt University (US), Curtin University (AU), National Radio Astronomy Observatory (US), Abington Memorial Hospital (US), Hillsdale College (US), Canadian Institute for Theoretical Astrophysics (CA), Max Planck Institute for Gravitational Physics (DE), Eureka Scientific (US), International Centre for Radio Astronomy Research (AU), University of Wisconsin–Milwaukee (US), University of Puerto Rico-Mayaguez (PR), University of Maryland, College Park (US), University of Montana (US), University of Birmingham (GB), Newcastle University (GB), Search for Extraterrestrial Intelligence (US), Universidad Nacional de La Plata (AR), University of Puerto Rico at Arecibo (PR)
Openalex Percentile: Top 37%
Pulsars and Gravitational Waves Research
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