Systematic effects from black hole-neutron star waveform model uncertainties on the neutron star equation of state

TL;DR

This study assesses how uncertainties in waveform models affect the measurement of neutron star properties in black hole-neutron star mergers, revealing that current models introduce significant systematic errors hindering accurate neutron star equation of state determination.

Contribution

It provides the first comparison of hybrid waveforms from two different NR codes and evaluates the impact of waveform uncertainties on parameter estimation.

Findings

Systematic errors dominate over statistical uncertainties in tidal deformability measurements.

Current waveform models are insufficient for precise neutron star equation of state extraction.

Significant improvements in waveform modeling are necessary for reliable astrophysical inferences.

Abstract

We identify various contributors of systematic effects in the measurement of the neutron star (NS) tidal deformability and quantify their magnitude for several types of neutron star - black hole (NSBH) binaries. Gravitational waves from NSBH mergers contain information about the components' masses and spins as well as the NS equation of state. Extracting this information requires comparison of the signal in noisy detector data with theoretical templates derived from some combination of post-Newtonian (PN) approximants, effective one-body (EOB) models and %analytic fits to numerical relativity (NR) simulations. The accuracy of these templates is limited by errors in the NR simulations, by the approximate nature of the PN/EOB waveforms, and by the hybridization procedure used to combine them. In this paper, we estimate the impact of these errors by constructing and comparing a set of PN-NR hybrid waveforms, for the first time with NR waveforms from two different codes, namely, SpEC and SACRA, for such systems. We then attempt to recover the parameters of the binary using two non-precessing template approximants. We find that systematic errors are too large for tidal effects to be accurately characterized for any realistic NS equation of state model. We conclude that NSBH waveform models must be significantly improved if they are to be useful for the extraction of NS equation of state information or even for distinguishing NSBH systems from binary black holes.