Test for LISA foreground Gaussianity and stationarity: galactic white-dwarf binaries

TL;DR

This paper introduces a novel test for analyzing the Gaussianity and stationarity of the unresolved galactic white-dwarf binary foreground in LISA data, crucial for accurate gravitational wave signal interpretation.

Contribution

It develops a new method to detect non-Gaussianity and non-stationarity in the LISA white-dwarf binary foreground using simulated signals and Galactic models.

Findings

Detected non-Gaussianity in the 2-10 mHz band after demodulation.

Identified a new analytical modulation caused by LISA's motion and source anisotropy.

Highlighted the importance of modeling deviations to avoid biases in data analysis.

Abstract

Upcoming space-based gravitational-wave detectors will be sensitive to millions and resolve tens of thousands of stellar-mass binary systems at mHz frequencies. The vast majority of these will be double white dwarfs in our Galaxy. The greatest part will remain unresolved, forming an incoherent stochastic foreground signal. Using state-of-the-art Galactic models for the formation and evolution of binary white dwarfs and accurate LISA simulated signals, we introduce a test for foreground Gaussianity and stationarity, building on methods available for ground-based detectors. We explain the observed non-stationarity with a new analytical modulation induced by the LISA constellation motion and the intrinsic anisotropy of the source distribution. By demodulating the foreground signal, we reveal a deviation from Gaussianity in the 2-10 mHz frequency band. Our finding is crucial to design faithful data models: the proposed method serves as a diagnostic and estimation tool to flag and model deviations, respectively. Neglecting them would introduce systematic biases on individual sources and astrophysical foregrounds parameter estimation, ultimately leading to inaccurate interpretation of the LISA data.