A new explosion mechanism of SNII is suggested in
my talk. The condition that “the timescale of electron capture
is shorter than the hydrodynamic (collapse) timescale” is
taken as the new criterion of the beginning for the fast collapse
of SN core. It is found that the fast collapsing core is only
a part of the iron core, rather than the whole iron core of the
presupernova. The prompt explosion mechanism is valid for the
rapid collapsing core.
Similar to an expansion in a “vacuum”, the temperature
and the corresponding energy of both the radiation field in the
outgoing shock wave and the neutrino flux will decrease until
their energy becomes down to lower than the bonding energy of
a nucleon for the iron group nucleus. The nuclei in the rest slowly
contracting iron core of the presupernova will not be disintegrated
by the both the gamma ray photons in the outgoing shock wave and
the neutrino in the neutrino flux. The rest slowly contracting
iron core, the mantle and the atmosphere of the presupernova will
be blown out by the radiation pressure of the outgoing shock wave
and by the kick of the neutrino flux through the interaction between
the neutrinos and the iron group nuclei. This is just the supernova
explosion.