Conversion of bulk kinetic energy into radiation in AGNs and GRBs: Particle transport effects

Free access article

Issue		A&A Volume 414, Number 2, February I 2004


Page(s)		463 - 474
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20031666

A&A 414, 463-474 (2004)
DOI: 10.1051/0004-6361:20031666

Conversion of bulk kinetic energy into radiation in AGNs and GRBs: Particle transport effects

R. Vainio^{1, 2}, M. Pohl³ and R. Schlickeiser³

¹ Space Research Laboratory (Part of Väisälä Institute for Space Physics and Astronomy, University of Turku.) , Department of Physics, 20014 University of Turku, Finland
² Theoretical Physics Division, Department of Physical Sciences, PO Box 64, 00014 University of Helsinki, Finland
³ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany

(Received 25 May 2002 / Accepted 9 October 2003 )

Abstract
We investigate the spatial structure of collisionless collision fronts in relativistic outflows interacting with ambient material. As a result of the interaction, ambient particles are picked up by the outflow and generate transverse plasma waves via streaming instabilities. Pick-up particle transport under the influence of self-generated turbulence inside such interaction regions is studied. We extend our previous momentum space modeling to include also a spatial dimension. We find that the following possibilities are consistent with quasi-linear equations of particle transport and wave generation: (i) if background waves have small intensities inside the outflow region, leading to inefficient scattering across the pitch-angle, $\theta$ , of $90^\circ$ , particles are isotropized in the backward hemisphere (relative to the outflow velocity vector) and self-generated waves have a steep, ${\propto} k^{-3}$ wavenumber spectrum; (ii) if background waves have large intensities, enabling particles to cross $\theta=90^\circ$ , particles can be fully isotropized. In case (i), however, the calculated self-generated wave amplitudes are close to the magnitude of the ordered field for reasonable choices of model parameters, giving the particles a chance to be scattered across the resonance gap by non-resonant processes. If the resonance gap is filled, a large fraction of the pick-up particles is expected to return to the upstream region, and an ultra-relativistic shock wave is predicted to form in front of the outflow, where the two relativistic particle populations (ambient and reflected) mix and form a relativistic plasma. Reflection of pick-up protons decreases the $\pi^0$ -decay luminosity of relativistic outflows, leading to a need to update parameters of previous modeling. An example of outflow parameters reproducing typical TeV-blazar observations is presented.

Key words: instabilities -- turbulence -- galaxies: BL Lacertae Objects: general -- gamma rays: theory -- shock waves

Offprint request: R. Vainio, rami.vainio@helsinki.fi

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