Description
I will present the analysis of the ringdown phase of the first
detected black-hole merger, GW150914, using a simulation-based
inference pipeline based on masked autoregressive flows. We obtain
approximate marginal posterior distributions for the ringdown
parameters, namely the mass, spin, and the amplitude and phases of the
dominant mode and its first overtone. Thanks to the locally amortized
nature of our method, we are able to calibrate our posteriors with
injected simulations, producing posterior regions with guaranteed
(i.e. exact) frequentist coverage of the true values. For GW150914,
our calibrated posteriors provide only mild evidence (~ 2 sigma) for
the presence of an overtone, even if the ringdown is assumed to start
at the peak of the amplitude.
