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Astron. Astrophys. 335, 26-32 (1998)

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Magnetic reconnection and particle acceleration in active galactic nuclei

R. Schopper, H. Lesch and G.T. Birk

Institut für Astronomie und Astrophysik der Universität München, Scheinerstrasse 1, D-81679 München, Germany

Received 16 February 1998 / Accepted 16 March 1998


Magnetic field-aligned electric fields are characteristic features of magnetic reconnection processes operating in externally agitated magnetized plasmas. An especially interesting environment for such a process are the coronae of accretion disks in active galactic nuclei (AGN). There, Keplerian shear flows perturb the quite strong disk magnetic field leading to intense current sheets. It was previously shown that given field strengths of 200 G in a shear flow, reconnection driven magnetic field aligned electric fields can accelerate electrons up to Lorentz factors of about 2000 in those objects thus providing us with a possible solution of the injection (pre-acceleration) problem. However, whereas in the framework of magnetohydrodynamics the formation of the field-aligned electric fields can be described consistently, the question has to be addressed whether the charged particles can really be accelerated up to the maximum energy supplied by the field-aligned electric potentials, since the accelerated particles undergo energy losses either by synchrotron or inverse Compton mechanisms. We present relativistic particle simulations starting from electric and magnetic fields obtained from magnetohydrodynamic simulations of magnetic reconnection in an idealized AGN configuration including nonthermal radiative losses. The numerical results prove that the relativistic electrons can be effectively accelerated even in the presence of an intense radiation bath. Energies from  [FORMULA] up to  [FORMULA] can be reached easily, depending on the energy density of the photon bath. The strong acceleration of the electrons mainly along the magnetic field lines leads to a very anisotropic velocity distribution in phase space. Not even an extremely high photon energy density is able to completely smooth the anisotropic pitch angle distribution which is characteristic for quasi monoenergetic particle beams.

Key words: acceleration of particles – MHD – galaxies: active – galaxies: nuclei

Send offprint requests to: R. Schopper

© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998