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Register a new userCoRe database of binary neutron star merger waveforms and its application in waveform development
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We present the Computational Relativity CoRe collaborations public database of gravitational waveforms from binary neutron star mergers. The database currently contains 367 waveforms from numerical simulations that are consistent with general relativity and that employ constraint satisfying initial data in hydrodynamical equilibrium. It spans 164 physically distinct configuration with different binary parameters (total binary mass, mass-ratio, initial separation, eccentricity, and stars spins) and simulated physics. Waveforms computed at multiple grid resolutions and extraction radii are provided for controlling numerical uncertainties. We also release an exemplary set of 18 hybrid waveforms constructed with a state-of-art effective-one-body model spanning the frequency band of advanced gravitational-wave detectors. We outline present and future applications of the database to gravitational-wave astronomy.
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Gravitational waves have been detected from the inspiral of a binary neutron-star, GW170817, which allowed constraints to be placed on the neutron star equation of state. The equation of state can be further constrained if gravitational waves from a post-merger remnant are detected. Post-merger waveforms are currently generated by numerical-relativity simulations, which are computationally expensive. Here we introduce a hierarchical model trained on numerical-relativity simulations, which can generate reliable post-merger spectra in a fraction of a second. Our spectra have mean fitting factors of 0.95, which compares to fitting factors of 0.76 and 0.85 between different numerical-relativity codes that simulate the same physical system. This method is the first step towards generating large template banks of spectra for use in post-merger detection and parameter estimation.
Gravitational waves emitted from the coalescence of neutron star binaries open a new window to probe matter and fundamental physics in unexplored, extreme regimes. To extract information about the supranuclear matter inside neutron stars and the properties of the compact binary systems, robust theoretical prescriptions are required. We give an overview about general features of the dynamics and the gravitational wave signal during the binary neutron star coalescence. We briefly describe existing analytical and numerical approaches to investigate the highly dynamical, strong-field region during the merger. We review existing waveform approximants and discuss properties and possible advantages and shortcomings of individual waveform models, and their application for real gravitational-wave data analysis.
We reanalyze gravitational waves from binary-neutron-star mergers GW170817 and GW190425 using a numerical-relativity (NR) calibrated waveform model, the TF2+_Kyoto model, which includes nonlinear tidal terms. For GW170817, by imposing a uniform prior on the binary tidal deformability $tilde{Lambda}$, the symmetric $90%$ credible interval of $tilde{Lambda}$ is estimated to be $481^{+436}_{-359}$ and $402^{+465}_{-279}$ for the case of $f_mathrm{max}=1000$ and $2048~mathrm{Hz}$, respectively, where $f_mathrm{max}$ is the maximum frequency in the analysis. We also reanalyze the event with other waveform models: two post-Newtonian waveform models (TF2_PNTidal and TF2+_PNTidal), the TF2+_NRTidal model that is another NR calibrated waveform model, and its upgrade, the TF2+_NRTidalv2 model. While estimates of parameters other than $tilde{Lambda}$ are broadly consistent among various waveform models, our results indicate that estimates of $tilde{Lambda}$ depend on waveform models. However, the difference is smaller than the statistical error. For GW190425, we can only obtain little information on the binary tidal deformability. The systematic difference among the NR calibrated waveform models will become significant to measure $tilde{Lambda}$ as the number of detectors and events increase and sensitivities of detectors are improved.
We present results from three-dimensional general relativistic simulations of binary neutron star coalescences and mergers using public codes. We considered equal mass models where the baryon mass of the two Neutron Stars (NS) is $1.4M_{odot}$, described by four different equations of state (EOS) for the cold nuclear matter (APR4, SLy, H4, and MS1; all parametrized as piecewise polytropes). We started the simulations from four different initial interbinary distances ($40, 44.3, 50$, and $60$ km), including up to the last 16 orbits before merger. That allows to show the effects on the gravitational wave phase evolution, radiated energy and angular momentum due to: the use of different EOSs, the orbital eccentricity present in the initial data and the initial separation (in the simulation) between the two stars. Our results show that eccentricity has a major role in the discrepancy between numerical and analytical waveforms until the very last few orbits, where tidal effects and missing high-order post-Newtonian coefficients also play a significant role. We test different methods for extrapolating the gravitational wave signal extracted at finite radii to null infinity. We show that an effective procedure for integrating the Newman-Penrose $psi_4$ signal to obtain the gravitational wave strain $h$ is to apply a simple high-pass digital filter to $h$ after a time domain integration, where only the two physical motivated integration constants are introduced. That should be preferred to the more common procedures of introducing additional integration constants, integrating in the frequency domain or filtering $psi_4$ before integration.
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