Method of Gravitational Wave Search Based on Adaptive Time-Frequency Analysis

The Hilbert-Huang transform (HHT) analysis has been developed as a method for time series analysis of nonlinear and nonstationary data, and it enables us to perform a high resolution time frequency analysis of signals with strong frequency modulation by evaluating the instantaneous variation of amplitude and frequency of data. Using the HHT, we analyze gravitational waves from late inspiral, merger, and post-merger phases of binary neutron stars (BNS) coalescence, computed by a general relativistic numerical simulation. We find that we can clearly observe the time evolution of the instantaneous frequency of the post-merger waveforms. This allows us to constrain the equation of state of neutron stars and to evaluate the radius with a few hundred meters accuracy if BNS coalescences occur within 10 Mpc. Moreover, we confirm the effectiveness of HHT by using real KAGRA test observation data.