Evidences for non-thermal X-ray emission from SNRs
have also indicated that high-energy electrons in the TeV
region are accelerated in the remnants (e.g. Koyama
et al., 1995). These observations strongly suggest that cosmic-
ray electrons are accelerated in SNRs and that SNRs
are the most likely primary sources of cosmic-ray electrons.
These accelerated electrons in SNRs should be liberated
from the remnants and propagate to the solar system
through the Galaxy. In a different scenario, high-energy
electrons and positrons are produced in the decay processes
p± ! l±! e± of pions resulting from nuclear interactions
of cosmic-ray nuclei with the interstellar medium.
Although in such processes the number of positrons is
almost equal to the electrons, the fraction of positrons is
approximately 10% of the electrons at energies of 1–
10 GeV region as indicated by present observations as
described in the Section 2. Therefore, one can conclude
that most electrons are originated from primary sources,
in which they are accelerated, and that approximately
10% of the electrons and possibly all positrons in cosmicrays
are from nuclear interactions in the interstellar
medium.