The NANOGrav 15-Year Data Set: Improved Timing Precision With VLBI Astrometric Priors
Abstract
Accurate pulsar astrometric estimates play an essential role in 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 sub-milliarcsecond astrometric estimations require years of observations and, even then, power from red noise can be inadvertently absorbed into astrometric parameter fits, biasing the resulting estimations and reducing our 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 calibrated a frame tie to account for the offsets between the reference frames used in VLBI and timing. Then, we used the VLBI-informed priors and timing-based likelihoods of several astrometric solutions consistent with both techniques 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 absorption of spectral power at 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.
Cite
@article{arxiv.2509.21203,
title = {The NANOGrav 15-Year Data Set: Improved Timing Precision With VLBI Astrometric Priors},
author = {Sofia V. Sosa Fiscella and Michael T. Lam and Gabriella Agazie and Akash Anumarlapudi and Anne M. Archibald and Zaven Arzoumanian and Paul T. Baker and Paul R. Brook and H. Thankful Cromartie and Kathryn Crowter and Maria Silvina De Biasi and Megan E. DeCesar and Paul B. Demorest and Timothy Dolch 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 Jeffrey S. Hazboun and Ross J. Jennings and Megan L. Jones and David L. Kaplan and Matthew Kerr and Duncan R. Lorimer and Jing Luo and Ryan S. Lynch and Alexander McEwen and Maura A. McLaughlin and Natasha McMann and Bradley W. Meyers and Cherry Ng and David J. Nice 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 Ann Schmiedekamp and Carl Schmiedekamp and Brent J. Shapiro-Albert and Ingrid H. Stairs and Kevin Stovall and Abhimanyu Susobhanan and Joseph K. Swiggum and Haley M. Wahl},
journal= {arXiv preprint arXiv:2509.21203},
year = {2025}
}