Magnetic coupling of a rotating black hole with its surrounding accretion disk

The effects of the magnetic coupling ( MC) of a rotating black hole (BH) with its surrounding accretion disk are discussed in detail in the following aspects: ( 1) The mapping relation between the angular coordinate on the BH horizon and the radial coordinate on the disk is modified based on a more reasonable configuration of magnetic field, and a condition for the coexistence of the Blandford-Znajek (BZ) and the MC process is derived. ( 2) The transfer direction of energy and angular momentum in the MC process is described equivalently by the corotation radius and by the flow of electromagnetic angular momentum and redshifted energy, where the latter is based on an assumption that the theory of the BH magnetosphere is applicable to both the BZ and MC processes. ( 3) The pro. le of the current on the BH horizon and that of the current density. owing from the magnetosphere onto the horizon are given in terms of the angular coordinate of the horizon. It is shown that the current on the BH horizon varies with the latitude of the horizon and is not continuous at the angular boundary between the open and closed magnetic field lines. (4) The MC effects on disk radiation are discussed, and a very steep emissivity is produced by the MC process, which is consistent with the recent XMM-Newton observation of the nearby bright Seyfert 1 galaxy MCG - 6-30-15 in a variety of parameters of the BH-disk system.