Constructing a gravitational wave analysis pipeline for extremely large mass ratio inspirals

TL;DR

This paper develops a hierarchical semi-coherent search pipeline for extremely large mass-ratio inspirals (XMRIs) tailored to space-based gravitational-wave detectors like TianQin, enabling effective detection and parameter estimation of these signals.

Contribution

It introduces the first dedicated pipeline combining a semi-coherent $ ext{F}$-statistic, particle swarm optimization, and a novel eccentricity estimation method for XMRIs.

Findings

Successfully recovers XMRI signals in simulated TianQin data.

Achieves high-precision parameter estimation with fractional uncertainties below 10^{-3}.

Validates the pipeline's effectiveness for future XMRI searches.

Abstract

Extremely large mass-ratio inspirals (XMRIs), consisting of a brown dwarf orbiting a supermassive black hole, emit long-lived and nearly monochromatic gravitational waves in the millihertz band and constitute a promising probe of strong-field gravity and black-hole properties. However, dedicated data-analysis pipelines for XMRI signals have not yet been established. In this work, we develop, for the first time, a hierarchical semi-coherent search pipeline for XMRIs tailored to space-based gravitational-wave detectors, with a particular focus on the TianQin mission. The pipeline combines a semi-coherent multi-harmonic $\mathcal{F}$-statistic with particle swarm optimization, and incorporates a novel eccentricity estimation method based on the relative power distribution among harmonics. We validate the performance of the pipeline using simulated TianQin data for a Galactic center XMRI composed of a brown dwarf and Sgr A*. For a three-month observation, the pipeline successfully recovers the signal and achieves high-precision parameter estimation, including fractional uncertainties of $<10^{-6}$ in the orbital frequency, $\lesssim10^{-3}$ in the eccentricity, $\lesssim2\times10^{-3}$ in the black-hole mass, and $\lesssim10^{-3}$ in the black-hole spin. Our framework establishes a practical foundation for future XMRI searches with space-based detectors and highlights the potential of XMRIs as precision probes of stellar dynamics and strong-field gravity in the vicinity of supermassive black holes.