Issues regarding the Blandford-Znajek process as a gamma-ray burst inner engine

Several issues regarding the Blandford-Znajek process are discussed to demonstrate that it can be an effective mechanism for powering gamma-ray bursts. Using a simple circuit analysis, it is argued that the disk power increases the effective power of the black hole accretion disk system, although a part of the disk power can be dissipated into black hole entropy. Within the framework of a force-free magnetosphere with a strong magnetic field, a magnetically dominated MHD flow is found to support the Blandford-Znajek process, and it is demonstrated that the possible magnetic repulsion by the rotating black hole will not affect the efficiency substantially.