  We investigate impacts of stellar rotation and magnetic fields on black hole
(BH) formation and its subsequent explosive activities, by conducting
axisymmetric radiation-magnetohydrodynamics simulations of gravitational
collapse of a 70 $M_\odot$ star with two-moment multi energy neutrino transport
in numerical relativity. Due to its dense stellar structure, all models cannot
avoid the eventual BH formation even though a strongly magnetized model
experiences the so-called magnetorotational explosion prior to the BH
formation. One intriguing phenomenon observed in the strongly magnetized model
is the formation of a relativistic jet in the post-BH formation. The
relativistic jet is the outcome of a combination of strong magnetic fields and
low-density materials above the BH. The jet further enhances the explosion
energy beyond $\sim10^{52}$ erg, which is well exceeding the gravitational
overburden ahead of the shock. Our self-consistent supernova models demonstrate
that rotating magnetized massive stars at the high-mass end of supernova
progenitors could be a potential candidate of hypernova and long gamma-ray
burst progenitors.
