Gravitational wave from GRB center: A black hole-torus system

Abstract

We discuss a possible gravitational wave radiation from a center of GRB, which consists of a rotating black hole and a torus. The gravitational waves can be generated by the precession as well as the local intrinsic inhomogeneity of the torus. Using the typical values relevant to GRB center, one can expect gravitational wave production with frequencies roughly in the range of 10 2 up to 10 3 Hz, which correspond basically to the Lense-Thirring frequency and the Keplerian frequency, respectively. For a rigid precession, the amplitude is found to be not smaller than the recent estimation for a precessing neutron star. For a Lense-Thirring precession, the line-broadening in the observed spectrum is expected due to the modulation of the torus orientation to the line of sight. The effect of the back reaction of gravitational radiation is estimated to be not so significant for long-duration GRBs.