Revisiting the ringdown of GW150914

Abstract

We examine recent claims that evidence for an overtone in the ringdown of the GW150914 binary black hole merger was a result of noise anomalies. We cannot reproduce these claims, finding that our previous analysis of this event is robust to data analysis choices and consistent with the expectation that strain after the peak is well described as a superposition of quasinormal modes of the remnant black hole. We discuss the meaning and implications of establishing that any specific ringdown mode was detected, and argue that it is misguided to expect actual LIGO-Virgo data to inform the discussion of whether or why the merger looks linear.