  We present results of 2D hydrodynamic simulations of stellar core collapse,
which confirm that the neutrino-heating mechanism remains viable for the
explosion of a wider mass range of supernova progenitors with iron cores. We
used an energy-dependent treatment of the neutrino transport based on the
"ray-by-ray plus" approximation, in which the number, energy, and momentum
equations are closed with a variable Eddington factor obtained by iteratively
solving a model Boltzmann equation. We focus on the evolution of a 15 Msun
progenitor and show that shock revival and the explosion are initiated at about
600 ms post bounce, powered by neutrino energy deposition. Similar to previous
findings for an 11.2 Msun star, but significantly later, the onset of the
explosion is fostered by the standing accretion shock instability (SASI). This
instability exhibits highest growth rates for the dipole and quadrupole modes,
which lead to large-amplitude bipolar shock oscillations and push the shock to
larger radii, thus increasing the time accreted matter is exposed to neutrino
heating in the gain layer. Therefore also convective overturn behind the shock
is strengthened. A "soft" nuclear equation of state that causes a rapid
contraction and a smaller radius of the forming neutron star and thus a fast
release of gravitational binding energy, seems to be more favorable for an
explosion. Rotation has the opposite effect because it leads to a more extended
and cooler neutron star and thus lower neutrino luminosities and mean energies
and overall less neutrino heating. Neutron star g-mode oscillations and the
acoustic mechanism play no important role in our simulations. (abridged)

Astrophysics