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Astron. Astrophys. 324, 395-409 (1997)

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-ray emission and spectral evolution of pair plasmas in AGN jets

I. General theory and a prediction for the GeV - TeV emission from ultrarelativistic jets

M. Böttcher , H. Mause and R. Schlickeiser

Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany

Received 25 March 1996 / Accepted 29 January 1997


The evolution of the particle distribution functions inside a relativistic jet containing an [FORMULA] - [FORMULA] pair plasma and of the resulting [FORMULA] -ray and X-ray spectra is investigated. The first phase of this evolution is governed by heavy radiative energy losses. For this phase, approximative expressions for the energy-loss rates due to inverse-Compton scattering, using the full Klein-Nishina cross section, are given as one-dimensional integrals for both cooling by inverse-Compton scattering of synchrotron photons (SSC) and of accretion disk photons (EIC).

We calculate instantaneous and time-integrated [FORMULA] -ray spectra emitted by such a jet for various sets of parameters, deducing some general implications on the observable broadband radiation. Finally, we present model fits to the broadband spectrum of Mrk 421. We find that the most plausible way to explain both the quiescent and the flaring state of Mrk 421 consists of a model where EIC and SSC dominate the observed spectrum in different frequency bands. In our model the flaring state is primarily related to an increase of the maximum Lorentz factor of the injected pairs.

Key words: plasmas – galaxies: jets – gamma-rays: theory

Send offprint requests to: M. Böttcher

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998