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Lookup NU author(s): Dr Anne ArchibaldORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2026. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the https://creativecommons.org/licenses/by/4.0/. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Pulsar timing arrays (PTAs) conduct low-frequency gravitational-wave (GW) 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 GWs 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 ∼1.5 solar cycles. We also find evidence for nondispersive 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 GW searches with PTAs.
Author(s): Larsen B, Baier JG, Oliver DJ, Wayt K, Chang Y-T, Hazboun JS, Mingarelli CMF, Simon J, Miles MT, Agazie G, Anumarlapudi A, Archibald AM, Arzoumanian Z, Baker PT, Brook PR, Cromartie HT, Crowter K, DeCesar ME, Demorest PB, Dolch T, Ferrara EC, Fiore W, Fonseca E, Freedman GE, Garver-Daniels N, Gentile PA, Glaser J, Good DC, Jennings RJ, Jones ML, Kaplan DL, Kerr M, Lam MT, Lorimer DR, Luo J, Lynch RS, McEwen A, McLaughlin MA, McMann N, Meyers BW, Ng C, Nice DJ, Pennucci TT, Perera BBP, Pol NS, Radovan HA, Ransom SM, Ray PS, Schmiedekamp A, Schmiedekamp C, Shapiro-Albert BJ, Stairs IH, Stovall K, Susobhanan A, Swiggum JK, Wahl HM
Publication type: Article
Publication status: Published
Journal: Astrophysical Journal
Year: 2026
Volume: 1005
Issue: 1
Print publication date: 01/07/2026
Online publication date: 22/06/2026
Acceptance date: 30/04/2026
Date deposited: 01/07/2026
ISSN (print): 0004-637X
ISSN (electronic): 1538-4357
Publisher: American Astronomical Society
URL: https://doi.org/10.3847/1538-4357/ae677c
DOI: 10.3847/1538-4357/ae677c
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