2001MNRAS.320..235C

We suggest that an extreme Kerr black hole with a mass ∼10⁶M_☉, a dimensionless angular momentum {formmu1} and a marginally stable orbital radius {formmu2} located in a normal galaxy may produce a γ-ray burst (GRB) by capturing and disrupting a star. During the capture period, a transient accretion disc is formed and a strong transient magnetic field ∼ {formmu3} lasting for {formmu4} may be produced at the inner boundary of the accretion disc. A large amount of rotational energy of the black hole is extracted and released in an ultrarelativistic jet with a bulk Lorentz factor Γ larger than 10³ via the Blandford-Znajek process. The relativistic jet energy can be converted into γ-radiation via an internal shock mechanism. The GRB duration should be the same as the lifetime of the strong transient magnetic field. The maximum number of sub-bursts is estimated to be {formmu5} because the disc material is likely to break into pieces with a size about the thickness of the disc h at the cusp {formmu6} The shortest risetime of the burst estimated from this model is ∼ {formmu7} The model GRB density rate is also estimated.