  We present observational confirmation of Hawking's black-hole area theorem
based on data from GW150914, finding agreement with the prediction with 97%
(95%) probability when we model the ringdown including (excluding) overtones of
the quadrupolar mode. We obtain this result from a new time-domain analysis of
the pre- and postmerger data. We also confirm that the inspiral and ringdown
portions of the signal are consistent with the same remnant mass and spin, in
agreement with general relativity.
