  The spectral amplitude of the merger-ringdown gravitational wave (GW) emitted
by a comparable mass-ratio black hole merger is modeled by the greybody factor
of the remnant black hole. We also include the post-Newtonian correction to the
greybody factor model. Our model includes only a few fitting parameters, which
could evade the overfitting issue. We perform the mass-spin inference from the
SXS data without tuning the data range of each SXS waveform. Also, we find that
the exponential damping in the ringdown spectral amplitude can be modeled well
with the exponential damping in the greybody factor at high frequencies. Our
findings could be consistent with a conjecture that the light ring of the
remnant black hole, which sources the ringdown, forms as early as during the
merger stage. We discuss the formation of the light ring in the static binary
solution as a first step towards the understanding of how the separation of
merging black holes may affect the formation of the light ring.
