Author: Koutarou Kyutoku
Abstract: We propose a possibility of ultra-relativistic electromagnetic counterparts to gravitational waves from binary neutron star mergers at nearly all the viewing angles. Mechanisms include the merger-shock propagation accelerating a smaller mass in the outer parts of the neutron star crust to a larger Lorentz factor with smaller energy. This mechanism is difficult to resolve by current 3D numerical simulations. The outflows emit synchrotron flares for seconds to days by shocking the ambient medium. Ultra-relativistic flares shine at an early time and in high energy bands, potentially detactable by current X-ray to radio instruments, such as Swift XRT and Pan-Starrs, and even in low ambient density by EVLA. The flares probe the merger position and time, and the merger types as black hole-neutron star outflows would be non/mildly-relativistic.