Transition from inspiral to plunge in numerical relativity simulations

We consider the evolution of the energy and angular momentum of quasicircular binaries during the transition to plunge in numerical simulations. By fitting the energy and angular momentum as functions of the frequency across mass ratios q=1 to q=20 we explore how well we can recover the small mass-ratio perturbative predictions. In particular we compare against two predictions for the binding energy: the prediction from the first law of binary mechanics (adiabatic) and the prediction from a two-timescale evolution (post-adiabatic). For frequencies close to the ISCO, fitting to an expansion in integer powers of the mass ratio becomes ineffective. When that is the case, we show that an expansion including fractional powers of the mass-ratio is more effective at recovering the leading small mass-ratio prediction.