Superradiance in a torus magnetosphere around a black hole

The coalescence of a neutron star and a black hole in a binary system is be lieved to form a torus around a,Kerr black hole. A similarly shaped magneto sphere then results from the remnant magnetic field of the neutron star. In the strong-field case, it contains a cavity for plasma waves Located betwe en the barrier of the gravitational potential and the surrounding torus. Th is cavity may be unstable to superradiance of electromagnetic waves. Superr adiant amplification of such waves, initially excited by turbulence in the torus, should inflate into a bubble in a time as short as similar to 0.75 ( 1 percent\epsilon\(2))(M/7M(.)) seconds similar to 0.15 to 1.5 seconds, ass uming an efficiency \epsilon\(2) = 0.5 to 5 percent and a mass M = 7M(.). T hese bubbles may burst and repeat, of possible relevance to intermittency i n cosmological gamma-ray bursts. The model predicts gamma-ray bursts to be anticorrelated with their gravitational wave emissions.