Non-Maxwellian electron distributions in clusters of galaxies
  Thermal X-ray spectra of clusters of galaxies and other sources are commonly
calculated assuming Maxwellian electron distributions. There are situations
where this approximation is not valid, for instance near interfaces of hot and
cold gas and near shocks. The presence of non-thermal electrons affects the
X-ray spectrum. To study the role of these electrons in clusters and other
environments, an efficient algorithm to calculate the X-ray spectra is needed.
We approximate an arbitrary electron distribution by the sum of Maxwellian
components. The decomposition is done using either a genetic algorithm or an
analytical approximation. The X-ray spectrum is then evaluated using a linear
combination of those Maxwellian components. Our method is fast and leads to an
accurate evaluation of the spectrum. The use of Maxwellian components allows to
use the standard collisional rates that are available in plasma codes such as
SPEX. We give an example of a spectrum for the supra-thermal electron
distribution behind a shock in a cluster of galaxies. The relative intensities
of the satellite lines in such a spectrum are sensitive to the presence of the
supra-thermal electrons. These lines can only be investigated with high
spectral resolution. We show that the instruments on future missions like
Astro-H and IXO will be able to demonstrate the presence or absence of these
supra-thermal electrons.
