  In this study we explore the magnetic mechanism of hypernovae and
relativistic jets of long duration gamma ray bursts within the collapsar
scenario. This is an extension of our earlier work [1]. We track the collapse
of massive rotating stars onto a rotating central black hole using axisymmetric
general relativistic magnetohydrodynamic code that utilizes a realistic
equation of state and takes into account the cooling associated with emission
of neutrinos and the energy losses due to dissociation of nuclei. The neutrino
heating is not included. We describe solutions with different black hole
rotation, mass accretion rate, and strength of progenitor's magnetic field.
Some of them exhibits strong explosions driven by Poynting-dominated jets with
power up to $12\times10^{51} {erg s}^{-1}$. These jets originate from the black
hole and powered via the Blandford-Znajek mechanism. A provisional criterion
for explosion is derived. A number of simulation movies can be downloaded from
http://www.maths.leeds.ac.uk/~serguei/research/movies/anim.html
