  We study the multimessenger signals from the merger of a black hole with a
magnetized neutron star using resistive magnetohydrodynamics simulations
coupled to full general relativity. We focus on a case with a 5:1 mass ratio,
where only a small amount of the neutron star matter remains post-merger, but
we nevertheless find that significant electromagnetic radiation can be powered
by the interaction of the neutron star's magnetosphere with the black hole. In
the lead-up to merger, strong twisting of magnetic field lines from the
inspiral leads to plasmoid emission and results in a luminosity in excess of
that expected from unipolar induction. We find that the strongest emission
occurs shortly after merger during a transitory period in which magnetic loops
form and escape the central region. The remaining magnetic field collimates
around the spin axis of the remnant black hole before dissipating, an
indication that, in more favorable scenarios (higher black hole spin/lower mass
ratio) with larger accretion disks, a jet would form.
