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Astron. Astrophys. 353, 473-478 (2000)

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Particle acceleration by rotating magnetospheres in active galactic nuclei

F.M. Rieger and K. Mannheim

Universitäts-Sternwarte, Geismarlandstrasse 11, 37083 Göttingen, Germany

Received 15 July 1999 / Accepted 20 October 1999

Abstract

We consider the centrifugal acceleration of charged test particles by rotating magnetospheres which are widely believed to be responsible for the relativistic jet phenomenon in active galactic nuclei (AGN). Based on an analysis of forces the equation for the radial accelerated motion is derived and an analytical solution presented under the assumption of an idealized spherical magnetosphere. We show that the rotational energy gain of charged particles moving outwards along rotating magnetic field lines is limited in general by (i) inverse-Compton losses in the radiation field of the disk in which 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 few hundred for the sub-Eddington conditions regarded to be typical for BL Lacs. In AGN with enhanced accretion rate the acceleration mechanism seems to be almost inefficient due to increasing inverse-Compton losses.

Key words: acceleration of particles – radiation mechanisms: non-thermal – gamma rays: theory – galaxies: active

Send offprint requests to: F.M. Rieger (frieger@uni-sw.gwdg.de)

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999
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