Monster radiative shocks in the perturbed magnetospheres of neutron stars

Magnetospheres of neutron stars can be perturbed by star quakes, interaction in a binary system, or sudden collapse of the star. The perturbations are typically in the kHz band and excite magnetohydrodynamic waves. We show that compressive magnetospheric waves steepen into monster shocks, possibly the strongest shocks in the universe. The shocks are radiative, i.e. the plasma energy is radiated before it crosses the shock. As the kHz wave with the radiative shock expands through the magnetosphere, it produces a bright X-ray burst. Then, it launches an approximately adiabatic blast wave, which will expand far from the neutron star. These results suggest a new mechanism for X-ray bursts from magnetars and support the connection of magnetar X-ray activity with fast radio bursts. Similar shocks may persistently occur in magnetized neutron-star binaries, generating an X-ray precursor of the binary merger. Powerful radiative shocks are also predicted in the magnetosphere of a neutron star when it collapses into a black hole, producing a bright X-ray transient.