  The gravitational radiation emitted during the merger of a black hole with a
neutron star is rather similar to the radiation from the merger of two black
holes when the neutron star is not tidally disrupted. When tidal disruption
occurs, gravitational waveforms can be broadly classified in two groups,
depending on the spatial extent of the disrupted material. Extending previous
work by some of us, here we present a phenomenological model for the
gravitational waveform amplitude in the frequency domain encompassing the three
possible outcomes of the merger: no tidal disruption, "mild" and "strong" tidal
disruption. The model is calibrated to 134 general-relativistic numerical
simulations of binaries where the black hole spin is either aligned or
antialigned with the orbital angular momentum. All simulations were produced
using the SACRA code and piecewise polytropic neutron star equations of state.
The present model can be used to determine when black-hole binary waveforms are
sufficient for gravitational-wave detection, to extract information on the
equation of state from future gravitational-wave observations, to obtain more
accurate estimates of black hole-neutron star merger event rates, and to
determine the conditions under which these systems are plausible candidates as
central engines of gamma-ray bursts, macronovae and kilonovae.
