Particle acceleration by rotating magnetospheres in active galactic nuclei

We consider the centrifugal acceleration of charged test particles by rotat ing magnetospheres which are widely believed to be responsible for the rela tivistic jet phenomenon in active galactic nuclei (AGN). Based on an analys is of forces the equation for the radial accelerated motion is derived and an analytical solution presented under the assumption of an idealized spher ical magnetosphere. We show that the rotational energy gain of charged part icles moving outwards along rotating magnetic field lines is limited in gen eral by (i) inverse-Compton losses in the radiation field of the disk in wh ich the magnetosphere is anchored and (ii) the breakdown of the bead-on-the -wire approximation which occurs in the vicinity of the light cylinder. The corresponding maximum Lorentz factor for electrons is of the order of a fe w hundred for the sub-Eddington conditions regarded to be typical for BL La cs. In AGN with enhanced accretion rate the acceleration mechanism seems to be almost inefficient due to increasing inverse-Compton losses.