Open AccessThermalization by synchrotron absorption in compact sources: electron and photon distributions
Author(s) -
Ghisellini G.,
Haardt F.,
Svensson R.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01442.x
Subject(s) - physics , synchrotron radiation , synchrotron , photon , electron , thermalisation , compton scattering , absorption (acoustics) , atomic physics , plasma , astrophysics , nuclear physics , optics
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.