Exact outer boundary conditions for gravitational perturbations of the Schwarzschild metric feature integral convolution between a time-domain boundary kernel and each radiative mode of the perturbation. For both axial (Regge-Wheeler) and polar (Zerilli) perturbations, we study the Laplace transform of such kernels as an analytic function of (dimensionless) Laplace frequency. We present numerical evidence indicating that each such frequency-domain boundary kernel admits a sum-of-poles representation. Our work has been inspired by Alpert, Greengard, and Hagstroms analysis of nonreflecting boundary conditions for the ordinary scalar wave equation.
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