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

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 107-108 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 rad 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 ≥2 M. 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(103) 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.