Towards gravitational wave parameter inference for binaries with an eccentric companion

TL;DR

This paper develops a comprehensive model for line-of-sight acceleration effects in gravitational wave signals from binary black holes in three-body systems, enabling better parameter inference and potential origin discrimination.

Contribution

It introduces a new curvature- and projection-dependent phase model for LOSA in GW signals, improving upon local-expansion methods and enabling constraints on tertiary parameters.

Findings

ET could detect a few to tens of such systems annually

Constraints can discriminate between dynamical and AGN origins

No LOSA evidence found in reanalysis of GW190814 and O4a events

Abstract

We introduce a complete model for dephasing due to line-of-sight acceleration (LOSA) in gravitational wave (GW) signals from stellar-mass binary black holes (BBHs) in three-body systems. Our prescription provides curvature- and projection-dependent phase features that are not recovered by local-expansion-based treatments. We perform parameter-space surveys and mock parameter inferences assuming the nominal sensitivity of the Einstein Telescope (ET) to identify the regime where the time-varying LOSA allows for separate constraints on the outer orbital parameters, in particular the tertiary mass and distance. We estimate that ET may detect a few to tens of such systems per year, provided that all binaries merge dynamically, and demonstrate that these constraints can be used to directly discriminate between a dynamical and AGN origin for BBHs. Finally, we reanalyse the GW190814 event and four O4a events finding no evidence for LOSA, with the previously claimed LOSA in GW190814 disappearing when a sufficiently long data segment is used.