Length requirements for numerical-relativity waveforms

One way to produce complete inspiral-merger-ringdown gravitational waveforms from black-hole-binary systems is to connect post-Newtonian (PN) and numerical-relativity (NR) results to create hybrid'' waveforms. Hybrid waveforms are central to the construction of some phenomenological models for gravitational-wave (GW) search templates, and for tests of GW search pipelines. The dominant error source in hybrid waveforms arises from the PN contribution, and can be reduced by increasing the number of NR GW cycles that are included in the hybrid. Hybrid waveforms are considered sufficiently accurate for GW detection if their mismatch error is below 3% (i.e., a fitting factor above 0.97). We address the question of the length requirements of NR waveforms such that the final hybrid waveforms meet this requirement, considering nonspinning binaries with q = M-2/M-1 is an element of [1, 4] and equal-mass binaries with chi = S-i/M-i(2) is an element of [-0.5, 0.5]. We conclude that, for the cases we study, simulations must contain between three (in the equal-mass nonspinning case) and ten (the chi = 0.5 case) orbits before merger, but there is also evidence that these are the regions of parameter space for which the least number of cycles will be needed.