Monster shocks and transient black hole pulsars from neutron star-black hole mergers

An excitation of a compact object magnetosphere can lead to a strongly radiating shockwave (dubbed as a "monster shock") which can power high-energy electromagnetic bursts. From GRMHD simulations of the merger of a high mass ratio neutron star-black hole binary, we observe that a strong disturbance in the circumbinary magnetosphere from the plunge of a magnetized neutron star to a black hole can develop into monster shocks. The post-merger magnetosphere around the remnant black hole undergoes a rapid transition into an inclined split-monopole configuration, and is dissipated by magnetic reconnections on rotating current sheets. We show that the balding remnant black hole exhibits a recently proposed "black hole pulsar" state, launching an exponentially decaying striped wind of plasma. Our study reveals a novel type of shock-powered and reconnection-driven transients associated with compact binary mergers.