Model-independent predictions of post-ringdown gravitational echoes

This note presents model-independent predictions for post-ringdown gravitational wave echoes in binary black hole (BBH) and supermassive black hole (SMBH) mergers. We provide falsifiable ranges for the first echo delay (Δt), amplitude ratio (A_eco/A_peak), quality factor (Q_eco), and damping factor (η), parametrized by the remnant mass and spin. Ready-to-use search grids are included for both current ground-based detectors (LIGO–Virgo–KAGRA) and the future LISA mission. The predictions are fully testable with existing public data (GWOSC) and do not assume or endorse any specific microscopic model. This work aims to guide systematic searches for echoes as new gravitational-wave events are detected.