Neural posterior estimation of Galactic Binary signals for the LISA mission

Abstract

ESA's LISA mission will open a new window onto the gravitational-wave sky by detecting signals from a wide variety of sources in the millihertz frequency band. Among these, galactic binaries are expected to be the most numerous sources observable by LISA. Their analysis and parameter estimation represent a significant challenge, as the signals are expected to strongly overlap in both the time and frequency domains. Conventional Bayesian inference approaches, such as Markov Chain Monte Carlo sampling, are difficult to scale to this setting due to the high dimensionality of the problem and the complicated likelihood landscape which can hinder convergence. In this work, we explore simulation-based inference as a means to perform efficient parameter estimation for single galactic binaries, with a potential extension to the analysis of multiple overlapping sources. Our approach relies on a conditional normalizing flow acting as a neural posterior estimator. The model is trained using samples generated according to a dedicated simulation framework that does not require any likelihood computation. Once trained, the neural posterior estimator enables the generation of thousands of posterior samples per second, again without explicit likelihood evaluation. We first present results for a single source in a narrow frequency band, and then extend the analysis to wider frequency ranges. As a proof of concept, we further investigate the more challenging case of two overlapping sources. These results demonstrate the potential of likelihood-free inference as a scalable alternative to conventional Markov chain Monte Carlo sampling for the analysis of LISA galactic binaries.