Disentangling Coalescing Neutron Star-White Dwarf Binaries for LISA

TL;DR

This paper models the formation and evolution of white dwarf-neutron star binaries for LISA, showing how GW signals can reveal system properties and constrain neutron star physics.

Contribution

It introduces detailed numerical models of WD-NS binaries, including mass transfer and finite-temperature effects, enabling identification and parameter estimation from GW data.

Findings

Evolutionary tracks in GW frequency-mass space are distinctive.

Precise chirp detection can determine NS mass within a few percent.

Dual-line GW observations can constrain neutron star equations-of-state.

Abstract

The prime candidate sources for the upcoming space-borne gravitational wave (GW) observatory LISA are the numerous Galactic tight binaries of white dwarfs (WDs) and neutron stars (NSs), many of which will coalesce and undergo mass transfer, leading to simultaneous emission of X-rays and GWs. Here, detailed and coherent numerical stellar models are explored for the formation and evolution of these systems, including finite-temperature effects and complete calculations of mass transfer from a WD to a NS accretor. Evolutionary tracks of characteristic strain amplitude are computed, and the unique pattern of their evolution in the GW frequency-dynamical chirp mass parameter space enables a firm identification of the nature of the systems. Furthermore, it is demonstrated that a precise detection of the chirp allows determination of the NS mass to an accuracy of a few per cent, with applications to constraining its equation-of-state, in particular for dual-line GW sources observed simultaneously at high and low frequencies.