POYNTING JETS FROM BLACK-HOLES AND COSMOLOGICAL GAMMA-RAY BURSTS

We discuss the properties of magnetically dominated jetlike outflows f rom stellar mass black holes surrounded by debris tori resulting from neutron star disruption. These jets may have narrow cores (along the r otation axis) that are almost free of baryons and attain very high bul k Lorentz factors greater than or similar to 10(6). The jets give rise to a characteristic MeV to TeV emission as well as to relativistic sh ocks producing the usual MeV bursts. Because the outflow is highly dir ectional, the properties of the observed gamma rays would depend on th e viewing angle relative to the rotation axis. Even for the most inten se bursts, which under the assumption of isotropic emission and substa ntial redshifts would be inferred to emit 10(52)-10(53) ergs, the effi ciencies required are only 10(-2) to 10(-4).