The NANOGrav 15 yr Data Set: Customized Chromatic Noise Models
Bjorn Larsen, Jeremy G. Baier, Daniel J. Oliver, Kalista Wayt, Yu-Ting Chang, Jeffrey S. Hazboun, Chiara M. F. Mingarelli, Joseph Simon, Matthew T. Miles, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Paul R. Brook, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Ross J. Jennings, Megan L. Jones, David L. Kaplan, Matthew Kerr, Michael T. Lam, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Alexander McEwen, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Cherry Ng, David J. Nice, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Ann Schmiedekamp, Carl Schmiedekamp, Brent J. Shapiro-Albert, Ingrid H. Stairs, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Haley M. Wahl
astro-ph.HE
Submitted: 2026-06-26
Comments: 50 pages, 21 figures. Published in ApJ
Journal ref: ApJ 1005 29 (2026)
Code: https://github.com/mermaid-js/mermaid
License: http://creativecommons.org/licenses/by/4.0/
The gist: Pulsar timing arrays conduct low-frequency gravitational wave searches, which require comprehensive accounting of various noise sources to achieve robust results.
Terminology
Abstract
Pulsar timing arrays conduct low-frequency gravitational wave searches, which require comprehensive accounting of various noise sources to achieve robust results. Interstellar propagation effects (e.g., dispersion and scattering) are especially complex noise sources, introducing chromatic delays that can reduce sensitivity to gravitational waves and bias their inference if left unmodeled. These delays also strongly depend on the line of sight properties to each individual pulsar. To address this, we present customized chromatic noise models for 67 pulsars in the NANOGrav 15 yr dataset. These models are selected from an expanded suite of Gaussian processes to simultaneously characterize multiple types of chromatic delays and are tailored to each pulsar's dataset. Alongside probing the interstellar medium, we use these models to infer the solar wind electron density over the course of about 1.5 solar cycles. We also find evidence for non-dispersive chromatic delays in 21 out of 67 NANOGrav pulsars. After applying our chromatic models, we observe significant impacts on the inference of achromatic noise in 19 out of 67 pulsars, finding in several cases that a previously significant achromatic noise process can be partially or entirely described as chromatic. These results demonstrate that refined noise modeling is essential to enhance the sensitivity and accuracy of low-frequency gravitational wave searches with pulsar timing arrays.
Sources
- The NANOGrav 15-year Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background
- JAXNS: a high-performance nested sampling package based on JAX
- The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
- The second data release from the European Pulsar Timing Array II. Customised pulsar noise models for spatially correlated gravitational waves
- BlackJAX: Composable Bayesian inference in JAX
- Recursive Pathways to Marginal Likelihood Estimation with Prior-Sensitivity Analysis
- Beyond diagonal approximations: improved covariance modeling for pulsar timing array data analysis
- The NANOGrav 12.5-year Data Set: Chromatic Noise Characterization & Mitigation with Time-Domain Kernels
- Optimising the MeerKAT Pulsar Timing Array and towards precision pulsar timing with SKA-mid
- Combining the second data release of the European Pulsar Timing Array with low-frequency pulsar data
- An unusual pulse shape change event in PSR J1713+0747 observed with the Green Bank Telescope and CHIME
- Measuring scattering variations in pulsar timing observations: A test of the fidelity of current methods
- The NANOGrav 15-Year Data Set: A Case Study for Simplified Dispersion Measure Modeling for PSR J1455-3330 and the Impact on Gravitational Wave Sensitivity
- Rapid Construction of Joint Pulsar Timing Array Datasets: The Lite Method
- Energetic Ceilings and Benchmarks of Astrophysical Gravitational-Wave Backgrounds
- The Indian Pulsar Timing Array Data Release 2: II. Customised Single-Pulsar Noise Analysis and Noise Budget
- The Nanohertz Gravitational Wave Astronomer
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