Parameter Estimation with Nonstationary Noise in Gravitational-wave Data

Abstract The sensitivity of gravitational-wave (GW) detectors is characterized by their noise curves, which determine the detector’s reach and ability to measure the parameters of astrophysical sources accurately. The detector noise is typically modeled as stationary and Gaussian for many practical purposes and is characterized by its power spectral density (PSD). However, due to environmental and instrumental factors, physical changes in the state of detectors may introduce nonstationarity into the noise. Misestimation of the noise behavior directly impacts the posterior width of the signal parameters. It becomes an issue for studies that depend on accurate localization volumes, such as (i) probing cosmological parameters (e.g., the Hubble constant) using cross-correlation methods with galaxies and (ii) doing electromagnetic follow-up using localization information from parameter estimation done from premerger data. We study the effects of dynamical noise on the parameter estimation of the GW events. We develop a new method to correct dynamical noise by estimating a locally valid pseudo-PSD normalized along a potential signal’s time–frequency track. We do simulations by injecting binary neutron star merger signals in various scenarios where the detector goes through a period of nonstationarity with reference noise curves of third-generation detectors (Cosmic Explorer, the Einstein telescope). As an example, for a source where mismodeling of the noise biases the signal-to-noise estimate by even 10%, one would expect the estimated sky localization to be either under- or overreported by ∼20%; errors like this, especially in low latency, could potentially cause follow-up campaigns to miss the actual source location.