paper

Thermalization by synchrotron absorption in compact sources: electron and photon distributions

arXiv:astro-ph/9712166 · doi:10.1046/j.1365-8711.1998.01442.x

Abstract

The high energy continuum in Seyfert galaxies and galactic black hole candidates is likely to be produced by a thermal plasma. There are difficulties in understanding what can keep the plasma thermal, especially during fast variations of the emitted flux. Particle-particle collisions are too inefficient in hot and rarefied plasmas, and a faster process is called for. We show that cyclo-synchrotron absorption can be such a process: mildly relativistic electrons thermalize in a few synchrotron cooling times by emitting and absorbing cyclo-synchrotron photons. The resulting equilibrium function is a Maxwellian at low energies, with a high energy tail when Compton cooling is important. Assuming that electrons emit completely self absorbed synchrotron radiation and at the same time Compton scatter their own cyclo-synchrotron radiation and ambient UV photons, we calculate the time dependent behavior of the electron distribution function, and the final radiation spectra. In some cases, the 2-10 keV spectra are found to be dominated by thermal synchrotron self-Compton process rather than by thermal Comptonization of UV disk radiation.

8pages, MN.sty, accepted for pubblication in MNRAS

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