Effective-one-body waveforms for binary neutron stars using surrogate models

Abstract

Gravitational-wave observations of binary neutron star systems can provide information about the masses, spins, and structure of neutron stars. However, this requires accurate and computationally efficient waveform models that take 1 s to evaluate for use in Bayesian parameter estimation codes that perform 10 7 − 10 8 waveform evaluations. We present a surrogate model of a nonspinning effective-one-body waveform model with = 2, 3, and 4 tidal multipole moments that reproduces waveforms of binary neutron star numerical simulations up to merger. The surrogate is built from compact sets of effective-one-body waveform amplitude and phase data that each form a reduced basis. We find that 12 amplitude and 7 phase basis elements are sufficient to reconstruct any binary neutron star waveform with a starting frequency of 10 Hz. The surrogate has maximum errors of 3.8% in amplitude (0.04% excluding the last 100M before merger) and 0.043 radians in phase. This leads to typical mismatches of 10 −5 -10 −4 for Advanced LIGO depending on the component masses, with a worst case match of 7 × 10 −4 when both stars have masses ≥ 2M . The version implemented in the LIGO Algorithm Library takes ∼ 0.07 s to evaluate for a starting frequency of 30 Hz and ∼ 0.8 s for a starting frequency of 10 Hz, resulting in a speed-up factor of O(10 3 ) relative to the original Matlab code. This allows parameter estimation codes to run in days to weeks rather than years, and we demonstrate this with a Nested Sampling run that recovers the masses and tidal parameters of a simulated binary neutron star system.

On the ambiguity in relativistic tidal deformability

“…The Λ GW for (say) a neutron star can then be computed from the standard tidal deformability together with Eq. (36), and the neutron star waveform, complete with tidal effects, can be generated with some confidence.…”

“…The basic observation is that, when tidal deformabilities are included in a waveform model in a reasonable way, one can expect the ambiguity in relating back to the equation of state to be a single number that can be measured by fitting the model to a binary black hole waveform. More traditional semi-analytic methods (e.g., [33][34][35][36]) rely on numerical simulations of neutron star mergers for calibration. The method proposed here calibrates with vacuum (black hole) simulations, which are computationally cheaper and hence more practical to perform in the challenging early-inspiral regime.…”

An architecture for efficient gravitational wave parameter estimation with multimodal linear surrogate models

“…Surrogate models have been applied to reproduce the radiation from complicated sources, including long duration signals [20,26], arbitrarily many harmonic modes [20,25], spinning binary systems [26,31], precessing binary systems [17,32], and neutron star models with tidal effects [33]. Moreover, as we describe in this paper, calculations that arise naturally in parameter estimation studies can be expressed in terms of simple, precomputed quantities constructed from the reduced-order representation.…”

Comprehensive comparison of numerical relativity and effective-one-body results to inform improvements in waveform models for binary neutron star systems

“…For tests involving the EOB adGSF + model we use the publicly available code of [57] that was also used to create the surrogate model in [64]. Note that this code differs from the EOB model described above in the pointparticle sector: (i) non-quasi-circular (NQC) corrections (the factor N m in the waveform modes of Eq.…”