## Positron propagation in semi-relativistic plasmas: particle spectra and the annihilation line shape
^{1} Centre d'Etude Spatiale des Rayonnements (CNRS/UPS), 9
av. Colonel-Roche, 31028 Toulouse Cedex, France^{2} present address: Max-Planck-Institut für
Extraterrestrische Physik, Postfach 1603, D-85740 Garching,
Germany
By solving the Fokker-Planck equation directly we examine the
effects of annihilation, particle escape and injection on the form of
a steady-state positron distribution in thermal hydrogen plasmas with
. The positron fraction considered is small
enough, so it does not affect the electron distribution which remains
Maxwellian. We show that the escape of positrons in the form of
electron-positron pairs and/or pair plasma, e.g. due to the diffusion
or radiation pressure, has an effect on the positron distribution
causing, in some cases, a strong deviation from a Maxwellian.
Meanwhile, the distortion of the positron spectrum due to only
annihilation is not higher than a few percent and the annihilation
line shape corresponds to that of thermal plasmas. Additionally, we
present accurate formulas in the form of a simple expression or a
one-fold integral for energy exchange rates, and losses due to Moller
and Bhabha scattering, -, Suggesting that annihilation features observed by
## Contents- 1. Introduction
- 2. The Fokker-Planck equation: positron spectrum
- 3. Reaction rate formalism
- 4. Coulomb collisions
- 5. Bremsstrahlung
- 6. Compton scattering
- 7. Annihilation rate and spectrum
- 8. Calculations and analysis
- 9. Nova Muscae and 1E 1740.7-2942
- 10. Conclusion
- Acknowledgements
- References
© European Southern Observatory (ESO) 1997 Online publication: May 5, 1998 |