Uncovering Stealth Bias in LISA observations of Double White Dwarf Binaries due to Tidal Coupling

TL;DR

This paper investigates how tidal interactions in double white dwarf binaries affect gravitational wave measurements by LISA, revealing a stealth bias in mass estimation that can impact astrophysical conclusions if uncorrected.

Contribution

It demonstrates that tidal effects cause biases in mass estimates and introduces a Bayesian method to better constrain system parameters, highlighting the importance of accounting for tides in LISA data analysis.

Findings

Tidal effects do not allow individual mass constraints but provide lower bounds on total mass.

Neglecting tidal effects biases chirp mass estimates upwards.

High SNR and frequency are needed to detect tidal influences on frequency derivatives.

Abstract

Double white dwarfs are important gravitational wave sources for LISA, as they are some of the most numerous compact systems in our universe. Here we consider finite-sized effects due to tidal interactions, as they are expected to have a measurable impact on these systems. Previous studies suggested that tidal effects would allow the individual masses to be measured, but there was a subtle error in those analyses. Using a fully Bayesian analysis we find that while tidal effects do not allow us to constrain the individual masses, they do yield informative lower bounds on the total mass of the system. Including tidal effects is crucial to the accuracy of our estimation of the chirp and total mass. Neglecting tidal effects leads to significant biases towards higher chirp masses, and we see that the lower bound of the total masses is biased towards a higher value as well. For many systems observed by LISA, tidal effects can lead to a "stealth" bias, since only the first derivative of the frequency can be measured. To separate tidal effects from the usual point particle decay we need to be able to measure the change in the second derivative of the frequency cause by the tides. This can only be done for high frequency systems observed with high signal-to-noise. The bias, if not accounted for, can have significant astrophysical implications; for example, it could lead to an incorrect estimation of the population of potential Type IA supernovae progenitors.