Measuring Gravitational-Wave Propagation Speed with Multimessenger Observations

A measurement of gravitational wave (GW) propagation speed is one of important tests of gravity in a dynamical regime. We report a method to measure the GW propagation speed by directly comparing arrival times of GWs, neutrinos from supernovae (SN), and photons from short gamma-ray bursts (SGRB). We found that the future multimessenger observations can test the GW propagation speed with the precision of ~ 10^(-16)-10^(-15), improving the previous suggestions by 9 — 10 orders of magnitude. We also propose a novel method that distinguishes the true signal due to the deviation of GW speed from the speed of light and the intrinsic time delay with compact binaries at cosmological distances.