A new representation of the Einstein evolution equations is presented that is first order, linearly degenerate and symmetric hyperbolic. This new system uses the generalized harmonic method to specify the coordinates, and exponentially suppresses all small short-wavelength constraint violations. Physical and constraint-preserving boundary conditions are derived for this system, and numerical tests that demonstrate the effectiveness of the constraint suppression properties and the constraint-preserving boundary conditions are presented.

The code used in [Phys. Rev. D 92, 124012 (2015)] erroneously computed the enthalpy at the center of the neutron stars. Upon correcting this error, density oscillations in evolutions of rotating neutron stars are significantly reduced (from ∼20% to ∼0.5%). Furthermore, it is possible to construct neutron stars with faster rotation rates.

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We present a reduced-order surrogate model of gravitational waveforms from non-spinning binary black hole systems with comparable to large mass-ratio configurations. This surrogate model, BHPTNRSur1dq1e4, is trained on waveform data generated by point-particle black hole perturbation theory (ppBHPT) with mass ratios varying from 2.5 to 10,000. BHPTNRSur1dq1e4 extends an earlier waveform model, EMRISur1dq1e4, by using an updated transition-to-plunge model, covering longer durations up to 30,500 m1 (where m1 is the mass of the primary black hole), includes several more spherical harmonic modes up to = 10, and calibrates subdominant modes to numerical relativity (NR) data. In the comparable mass-ratio regime, including mass ratios as low as 2.5, the gravitational waveforms generated through ppBHPT agree surprisingly well with those from NR after this simple calibration step. We also compare our model to recent SXS and RIT NR simulations at mass ratios ranging from 15 to 32, and find the dominant quadrupolar modes agree to better than ≈ 10 −3 . We expect our model to be useful to study intermediate-mass-ratio binary systems in current and future gravitational-wave detectors.

Quasinormal mode (QNM) modeling is an invaluable tool for characterizing remnant black holes, studying strong gravity, and testing general relativity. Only recently have QNM studies begun to focus on multimode fitting to numerical relativity strain waveforms. As gravitational wave observatories become even more sensitive they will be able to resolve higher-order modes. Consequently, multimode QNM fits will be critically important, and in turn require a more thorough treatment of the asymptotic frame at I þ . The first main result of this work is a method for systematically fitting a QNM model containing many modes to a numerical waveform produced using Cauchy-characteristic extraction (CCE), a waveform extraction technique which is known to resolve memory effects. We choose the modes to model based on their power contribution to the residual between numerical and model waveforms. We show that the allmode strain mismatch improves by a factor of ∼10 5 when using multimode fitting as opposed to only fitting the ð2; AE2; nÞ modes. Our most significant result addresses a critical point that has been overlooked in the QNM literature: the importance of matching the Bondi-van der Burg-Metzner-Sachs (BMS) frame of the numerical waveform to that of the QNM model. We show that by mapping the numerical waveformswhich exhibit the memory effect-to a BMS frame known as the super rest frame, there is an improvement of ∼10 5 in the all-mode strain mismatch compared to using a strain waveform whose BMS frame is not fixed. Furthermore, we find that by mapping CCE waveforms to the super rest frame, we can obtain allmode mismatches that are, on average, a factor of ∼4 better than using the publicly available extrapolated waveforms. We illustrate the effectiveness of these modeling enhancements by applying them to families of waveforms produced by numerical relativity and comparing our results to previous QNM studies.

A recent paper (Ajith et al 2012 Class. Quantum Grav. 29 124001) described a catalog of 56 hybrid post-Newtonian/numerical-relativity waveforms modeling the inspiral, merger and ringdown of binary black hole systems spanning a range of mass ratios and spins. This catalog has been created and validated for use in the NINJA-2 project to study the sensitivity of gravitational-wave search and parameter-estimation algorithms. The contents of this catalog are being made available for public use. This addendum describes the public release.

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Gravitational wave observations of large mass ratio compact binary mergers like GW190814 highlight the need for reliable, high-accuracy waveform templates for such systems. We present NRHybSur2dq15, a new surrogate model trained on hybridized numerical relativity (NR) waveforms with mass ratios q ≤ 15, and aligned spins |χ1z| ≤ 0.5 and χ2z = 0. We target the parameter space of GW190814-like events as large mass ratio NR simulations are very expensive. The model includes the (2,2), (2,1), (3,3), (4,4), and (5,5) spin-weighted spherical harmonic modes, and spans the entire LIGO-Virgo bandwidth (with f low = 20 Hz) for total masses M 9.5 M . NRHybSur2dq15 accurately reproduces the hybrid waveforms, with mismatches below ∼ 2 × 10 −3 for total masses 10 M ≤ M ≤ 300 M . This is at least an order of magnitude improvement over existing semianalytical models for GW190814-like systems. Finally, we reanalyze GW190814 with the new model and obtain source parameter constraints consistent with previous work.