  On September 18, 2022, an alert by ceCube indicated that a ~170TeV neutrino
arrived in directional coincidence with the blazar TXS 0506+056. This event
adds to two previous ones: a neutrino alert from its direction on September 22,
2017, and a 3sigma signature of a dozen neutrinos in 2014/2015. deBruijn 2020
showed that these two previous neutrino emission episodes could be due to a
supermassive binary black hole (SMBBH) where jet precession close to final
coalescence results in periodic emission. This model predicted a new emission
episode consistent with the September 18, 2022 neutrino observation. Here, we
show that the neutrino cadence of TXS 0506+056 is consistent with a SMBBH
origin with mass ratios q<0.3 for a total black hole mass of M>3e8Msun. For the
first time, we calculate the characteristic strain of the gravitational wave
emission of the binary, and show that the merger could be detectable by LISA
for black hole masses <5e8Msun if the mass ratios are in the range 0.1<q<0.3.
We predict that there can be a neutrino flare existing in the still to be
analyzed IceCube data peaking some time between 08/2019 and 01/2021 if a
precessing jet is responsible for all three detected emission episodes. The
next flare is expected to peak in the period 01/2023 to 08/2026. Further
observation will make it possible to constrain the mass ratio as a function of
the black hole mass more precisely and would open the window toward the
preparation of the detection of SMBBH mergers.
