Complex electron energy distributions in supernova remnants with non-thermal X-rays

Abstract

We address the problem of the diffusive acceleration of electrons in shocks of supernova remnants with nonthermal X-ray emission. A complex electron energy distribution develops, with energies within the range of thermal to highly relativistic energies. Starting from a Maxwellian distribution, drift acceleration produces, within the finite-size layer of the shock, a steep power-law supra-thermal electron energy distribution. Diffusive shock acceleration then produces an ˜ E‑2.42±0.04 spectrum (Biermann, 1993). We find that at higher energies the spectrum steepens, due to the existence of the individual blob shocks and the substructure of the shock region (observed in radio emission). We discuss the consequences of this for X-ray emission in SNRs showing non-thermal emission. This may be a paradigm for acceleration of energetic electrons also in other astrophysical sites, such as clusters of galaxies.