PARTICLE-ACCELERATION BY MAGNETIC FIELD-ALIGNED ELECTRIC-FIELDS IN ACTIVE GALACTIC NUCLEI

We show that the formation of magnetic field-aligned electric fields E -parallel to explains the existence of relativistic leptons with Loren tz factors less than about 2000 in active galactic nuclei. This Lorent z factor is the minimum value for Fermi processes to accelerate lepton s. This is also known as the injection problem: particles with gamma < 2000 cannot be accelerated by shock waves or MHD turbulence, also kno wn as Fermi I and II mechanisms. E-parallel to can accelerate charged particles very efficiently on very short time scales. The appearance o f such magnetic field-aligned electric fields is an implicit property of magnetized, turbulent plasmas in which the electrical conductivity is not infinitely high. We describe the appearance of these fields wit hin an analytical kinematic approach as well as on the grounds of a nu merical dynamical model. Due to the small spatial extension of such la yers the acceleration time is much shorter than the energy loss time d ue to inverse Compton scattering of the UV radiation of the underlying accretion disk. Thus: relativistic leptons can be effectively produce d in the corona of an accretion disk even in the presence of an intens e radiation bath. This is an important result for gamma-ray models, wh ich require a high initial density of leptons with Lorentz factors of about 10(3).