  The recently established formalism of a worldline quantum field theory, which
describes the classical scattering of massive bodies in Einstein gravity, is
generalized up to quadratic order in spin -- for a pair of Kerr black holes
revealing a hidden ${\mathcal N}=2$ supersymmetry. The far-field time-domain
waveform of the gravitational waves produced in such a spinning encounter is
computed at leading order in the post-Minkowskian (weak field, but generic
velocity) expansion, and exhibits this supersymmetry. From the waveform we
extract the leading-order total radiated angular momentum in a generic
reference frame, and the total radiated energy in the center-of-mass frame to
leading order in a low-velocity approximation.
