Gauge-Invariant Gravitational Wave Extraction from Coalescing Binary Neutron Stars

We report application of a method for extracting gravitational waves to three-dimensional numerical simulation on coalescing binary neutron stars. We found the extracted wave form includes the componets corresponding to the quadrupole part in the Newtonian potential of the background metric, if it is monitored at a position not far from the central stars. We present how to eliminate it.