Searching for gravitational wave echoes in GWTC-1 and O3 events.

Gravitational wave (GW) echoes, if they exist, would be a probe to the near-horizon physics of black hole. In this brief report, we performed the Monte Carlo Markov Chain analysis to search for echo signal in all GWTC-1 and O3 GW events. We focus on the Insprial-Merger-Ringdown-Echo (IMRE) waveform, and apply the Bayesian model selection to compare the IMRE result with IMR's (no echo). We find no statistically significant ($<1\sigma$ combined) evidence for the GW echoes and only individual GW events with the echoes at $1\sim 2\sigma$ significance.