Journal Article

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

G. Ghisellini, F. Haardt and R. Svensson

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 297, issue 2, pages 348-354
Published in print June 1998 | ISSN: 0035-8711
Published online June 1998 | e-ISSN: 1365-2966 | DOI:
Thermalization by synchrotron absorption in compact sources: electron and photon distributions

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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 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 behaviour of the electron distribution function, and the final radiation spectra. In some cases, the 2–10 keV spectra are found to be dominated by the thermal synchrotron self-Compton process rather than by thermal Comptonization of UV disc radiation.

Keywords: radiation mechanisms: thermal; galaxies: Seyfert; X-rays: galaxies

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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