GW190521: Quantifying the Evidence for Near-Horizon Quantum effects

The exceptionally loud ringdown of GW190521 makes it an ideal candidate to search for gravitational wave echoes, a proposed smoking gun for the quantum structure of black hole horizons. We perform an unprecedented multi-pronged search for echoes via two well-established and independent pipelines: a template-based search for stimulated emission of Hawking radiation (or Boltzmann echoes), and the model-agnostic coherent WaveBurst (cWB) search. Given GW190521 parameters, stimulated Hawking radiation from the merger is expected to lead to post-merger echoes at horizon mode frequency of ~ 50 Hz, repeating at intervals of ~ 1 second, due to partial reflection off Planckian quantum structure of the horizon. In this talk, I will be presenting the results found when performing two independent searches and discussing their results. I will argue how both methods agree on the existence of evidence in favor of echoes and also their agreement in the echo parameters. The statistical significance of these findings will also be discussed.