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

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9. Summary and conclusions

We gave a detailed discussion of the various radiative energy loss mechanisms acting in relativistic pair plasmas and concentrated on the application to jets from active galactic nuclei. In the first phase after the acceleration or injection of pairs radiative cooling due to inverse-Compton scattering is the dominant process. Here, Klein-Nishina effects are much more pronounced for inverse-Compton scattering of external radiation (from the central accretion disk) than for the SSC process since the synchrotron spectrum extends over a much broader energy distribution, allowing for efficient Thomson scattering at all particle energies.

We developed a computer code which allows to follow the evolution of the energy distributions of electrons/positrons self-consistently, accounting for all Klein-Nishina effects and for the time-dependence of the synchrotron, SSC and external radiation fields which contribute to the radiative cooling of the pairs and computing the instantaneous [FORMULA] -ray production from the resulting pair distributions. Since the intrinsic cooling timescales are much shorter than the time resultion of present-day instruments, we calculated time-integrated spectra and compared them to observations.

We found some general results from a series of different simulations:

(a) Due to the short cooling times involved in the SSC radiation mechanism, implying that we only see time-integrated SSC emission leading to an overprediction of hard X-ray flux from blazars, we favor EIC to be the dominant radiation process in [FORMULA] -ray blazars.

(b) Detailed simulations show that the EIC spectrum of a cooling ultrarelativistic pair distribution with maximum energies implying EIC scattering in the Klein-Nishina regime is harder in the case of pure Thomson scattering where we recover the classical results of Dermer & Schlickeiser (1993 a).

(c) The low-energy cutoff in the synchrotron spectra from dense pair jets is not determined by synchrotron self-absorption, but by the Razin-Tsytovich effect. Only when the jet widens up, radio emission at [FORMULA] Hz can escape the jet.

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998