  Using axisymmetric simulations coupling special relativistic MHD, an
approximate post-Newtonian gravitational potential and two-moment neutrino
transport, we show different paths for the formation of either protomagnetars
or stellar mass black holes. The fraction of prototypical stellar cores which
should result in collapsars depends on a combination of several factors, among
which the structure of the progenitor star and the profile of specific angular
momentum are probably the foremost. Along with the implosion of the stellar
core, we also obtain supernova-like explosions driven by neutrino heating and
hydrodynamic instabilities or by magneto-rotational effects in cores of
high-mass stars. In the latter case, highly collimated, mildly relativistic
outflows are generated. We find that after a rather long post-collapse phase
(lasting >~ 1 sec) black holes may form in cases both of successful and failed
supernovalike explosions. A basic trend is that cores with a specific angular
momentum smaller than that obtained by standard, one-dimensional stellar
evolution calculations form black holes (and eventually collapsars).
Complementary, protomagnetars result from stellar cores with the standard
distribution of specific angular momentum obtained from prototypical stellar
evolution calculations including magnetic torques and moderate to large mass
loss rates.
