Gamma-ray bursts and gravitational radiation from black hole-torus systems

Cosmological gamma-ray bursts (GRBs) are probably powered by systems harboring a rotating black hole. These may result from hypernovae or black hole-neutron star coalescence. We identify short/long bursts with hyper- and suspended-accretion states around slowly/rapidly spinning black holes. Baryon poor jets, as input to the observed GRB/afterglow emissions, may result from dissipation in a gap along an open flux-tube on the axis of rotation of the black hole. The torus is expected to radiate a major fraction of the black hole luminosity into gravitational waves, which suggests that long GRBs may be the most powerful LIGO/VIRGO burst sources in the Universe. (Abbreviated)