Echoes from the Abyss: A Status Update
  Gravitational wave echoes provide our most direct and surprising
observational window into quantum nature of black holes. Three years ago, the
first search for echoes from Planck-scale modifications of general relativity
near black hole event horizons led to tentative evidence at false detection
probability of 1\% arXiv:1612.00266 . The study introduced a naive
phenomenological model and used the public data release by the Advanced LIGO
gravitational wave observatory for the first observing run O1 (GW150914,
GW151226, and LVT151012, now GW151012). Here, we provide a status update on
various observational searches for echoes by independent groups, and argue that
they can all be consistent if echoes are most prominent at lower frequencies
and/or in binary mergers of more extreme mass ratio. We also point out that the
only reported "detection" of echoes (with $>4\sigma$ confidence) at 1.0 second
after the binary neutron star merger GW170817 arXiv:1803.10454 is coincident
with the formation time of the black hole inferred from electromagnetic
observations.
