The most likely sources of high-energy cosmic-ray electrons in supernova remnants

Evidence of nonthermal X-ray emission and TeV gamma rays from supernova remnants (SNRs) have strengthened the hypothesis that primary Galactic cosmic-ray electrons are accelerated in SNRs. High-energy electrons lose energy via synchrotron and inverse Compton processes during propagation in the Galaxy. Because of these radiative losses, TeV electrons liberated from SNRs at distances larger than ∼1 kpc, or times older than ∼10⁵ yr, cannot reach the solar system. We investigated the cosmic-ray electron spectrum observed in the solar system using an analytical method and considered several candidate sources among nearby SNRs that may contribute to the high-energy electron flux. In particular, we discuss the effects for the release time from SNRs after the explosion, as well as the deviation of a source spectrum from a simple power law. From this calculation, we found that some nearby sources, such as Vela, Cygnus Loop, or Monogem, could leave unique signatures in the form of identifiable structure in the energy spectrum of TeV electrons and show anisotropies toward the sources, depending on when the electrons were liberated from the remnant. This suggests that, in addition to providing information on the mechanisms of acceleration and propagation of cosmic rays, specific cosmic-ray sources can be identified through the precise electron observation in the TeV region.