Estimation of starting times of quasinormal modes in ringdown gravitational waves with the Hilbert-Huang transform

Understand

It is known that a quasinormal mode (QNM) of a remnant black hole dominates a ringdown gravitational wave (GW) in a binary black hole (BBH) merger.

• To study properties of the QNMs, it is important to determine the time when the QNMs appear in a GW signal as well as to calculate its frequency and amplitude.
• In this paper, we propose a new method of estimating the starting time of the QNM and calculating the QNM frequency and amplitude of BBH GWs.
• We apply it to simulated merger waveforms by numerical relativity and the observed data of GW150914.