High-accuracy high-mass ratio simulations for binary neutron stars and their comparison to existing waveform models

Abstract

The subsequent observing runs of the advanced gravitational-wave detector network will likely provide us with various gravitational-wave observations of binary neutron star systems. For an accurate interpretation of these detections, we need reliable gravitational-wave models. To test and to point out how existing models could be improved, we perform a set of high-resolution numericalrelativity simulations for four different physical setups with mass ratios q = 1.25, 1.50, 1.75, 2.00, and total gravitational mass M = 2.7M . Each configuration is simulated with five different resolutions to allow a proper error assessment. Overall, we find approximately 2nd order converging results for the dominant (2,2), but also subdominant (2,1), (3,3), (4,4) modes, while, generally, the convergence order reduces slightly for an increasing mass ratio. Our simulations allow us to validate waveform models, where we find generally good agreement between state-of-the-art models and our data, and to prove that scaling relations for higher modes currently employed for binary black hole waveform modeling also apply for the tidal contribution. Finally, we also test if the current NRTidal model to describe tidal effects is a valid description for high-mass ratio systems. We hope that our simulation results can be used to further improve and test waveform models in preparation for the next observing runs.

Second release of the CoRe database of binary neutron star merger waveforms

“…In the following, we give an overview of the database content and outline the connections between physics and waveform morphology. The database contains waveforms from binaries with total masses ranging from 2.4 M ⊙ to around ∼3.4 M ⊙ with 45 datasets reaching mass ratios larger than q ≳ 1.4 and up to q = 2.1 [47,58,64]. EOS effect can be summarized to some extent 15 by the quadrupolar tidal polarizability parameters Λ 1,2 [71], where larger (smaller) values of Λ i are associated to stiffer (softer) EOSs.…”

“…Extreme mass ratios q ∼ 2 and NS rotation close to the breakup limit remain challenging to simulate as well as to obtain clean convergence in GW higher (subdominant) modes like (ℓ, m) = (2, 1), (3,3) and (4,4). Work in these directions is ongoing [58,62,64,65]. For example, clear fourth order convergence in the subdominant (3, 2) and (4, 4) modes for q = 1 has been shown in [65].…”

“…The new release includes GW strains and Weyl multipoles information up to the (ℓ, m) = (4, 4) mode. The new data were computed in simulations presented in references [54][55][56][57][58][59][60][61][62][63][64][65][66] and include BNS waveforms consistent with the GW events GW170817 [56,58,59,67] and GW190425 [66,68].…”