Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Positron propagation in semi-relativistic plasmas: particle spectra and
  the annihilation line shape   By solving the Fokker-Planck equation directly we examine effects of
annihilation, particle escape and injection on the form of a steady-state
positron distribution in thermal hydrogen plasmas with $kT<m_ec^2$. We show
that the escape of positrons in the form of electron-positron pairs and/or pair
plasma has an effect on the positron distribution causing, in some cases, a
strong deviation from a Maxwellian. Additionally, we present accurate formulas
for energy exchange rates, and losses due to Coulomb scattering,
bremsstrahlung, and Compton scattering in the Klein-Nishina regime. Suggesting
that annihilation features observed by SIGMA telescope from Nova Muscae and the
1E 1740.7-2942 are due to the positron/electron slowing down and annihilation
in thermal plasma, the electron number density and the size of the emitting
regions have been estimated. We show that in the case of Nova Muscae the
observed radiation is coming from a pair plasma stream ($n_{e^+}\approx
n_{e^-}$) rather than from a gas cloud. We argue that two models are probably
relevant to the 1E 1740.7-2942 source: annihilation in (hydrogen) plasma
$n_{e^+}\la n_{e^-}$ at rest, and annihilation in the pair plasma stream, which
involves matter from the source environment.

36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph