Arrival times of gravitational radiation peaks for binary inspiral

Modeling of gravitational waves (GWs) from binary black hole inspiral brings together early post-Newtonian waveforms and late quasinormal ringing waveforms. Attempts to bridge the two limits without recourse to numerical relativity involve predicting the time of the peak GW amplitude. This prediction will require solving the question of why the peak of the "source," i.e., the peak of the binary angular velocity, does not correspond to the peak of the GW amplitude. We show here that this offset can be understood as due to the existence of two distinct components of the radiation: the "direct" radiation analogous to that in flat spacetime and "scattered" radiation associated with curved spacetime. The time dependence of these two components and of their relative phases determines the location of the peak amplitude. We use a highly simplified model to clarify the two-component nature of the source, then demonstrate that the explanation is valid also for an extreme mass-ratio binary inspiral.