High-accuracy waveforms for black hole-neutron star systems with spinning black holes

TL;DR

This paper provides highly accurate numerical waveforms for black hole-neutron star systems, including spinning and precessing cases, and evaluates the performance of analytical models against these new benchmarks.

Contribution

The authors present the first long, accurate waveforms for BHNS binaries with spinning black holes and perform detailed comparisons of waveform extrapolation methods and model faithfulness.

Findings

Waveforms have <0.1 rad phase error during inspiral

Models perform well for face-on binaries (F>0.99)

Discrepancies increase for edge-on and precessing systems

Abstract

The availability of accurate numerical waveforms is an important requirement for the creation and calibration of reliable waveform models for gravitational wave astrophysics. For black hole-neutron star binaries, very few accurate waveforms are however publicly available. Most recent models are calibrated to a large number of older simulations with good parameter space coverage for low-spin non-precessing binaries but limited accuracy, and a much smaller number of longer, more recent simulations limited to non-spinning black holes. In this paper, we present long, accurate numerical waveforms for three new systems that include rapidly spinning black holes, and one precessing configuration. We study in detail the accuracy of the simulations, and in particular perform for the first time in the context of BHNS binaries a detailed comparison of waveform extrapolation methods to the results of Cauchy Characteristic Extraction. The new waveforms have $<0.1\,{\rm rad}$ phase errors during inspiral, rising to $\sim (0.2-0.4)\,{\rm rad}$ errors at merger, and $\lesssim 1\%$ error in their amplitude. We compute the faithfulness of recent analytical models to these numerical results, and find that models specifically designed for BHNS binaries perform well ($F>0.99$) for binaries seen face-on. For edge-on observations, particularly for precessing systems, disagreements between models and simulations increase, and models that include precession and/or higher-order modes start to perform better than BHNS models that currently lack these features.