Probing chromatic onsets of gravitational wave overtones

The ringdown data of both GW150914 and GW190521\_074359 (GW190521r) show evidence supporting the presence overtone. Previous studies all adopt a fundamental assumption, which were motivated more by convenience than first principles, that overtone mode share same onset. In this work, for time we relax such aim to probe possible chromatic onsets these two components within GW190521r data. For events, bound onset lags be $\Delta t_0\geq 5M_f$ at probabilities $\geq 94.7\%$, where $M_f$ is mass remnant black hole formed in merger. This result moderately favours non-simultaneous excitation between ringdown.