Renewed significance and spectral characterization of the NANOGrav gravitational wave background with better noise models

Pulsar timing array datasets like the NANOGrav 15-year release are building compelling evidence for a nanohertz gravitational wave (GW) background, offering insights into sources such as inspiralling supermassive black hole binaries. However, noise remains a major obstacle, and inaccurate noise models can bias GW measurements. Given the non-uniformity of pulsar time series and the diversity of intrinsic and environmental noise characteristics, we develop tailored noise models for each pulsar using a multi-step Bayesian approach. This includes searches for non-dispersive, radio-frequency dependent noise from the interstellar medium. These are effects often overlooked in standard models. We tailor the noise models of all of our pulsars and demonstrate improved mitigation using diagnostic tools. Enhanced spectral characterization of pulsar noise is crucial for refining GW background measurements and getting a cleaner picture of the detection significance.