Nonlinear diffusive shock acceleration of cosmic rays: quasi-thermal and non-thermal particle distributions

Abstract

Diffusive shock acceleration (DSA) of particles at collisionless shocks is the major accepted paradigm about the origin of cosmic rays (CRs). As a theory, it was developed during the late 1970s in the so-called test-particle case. If one considers the influence of CR particles at shock structure, then we are talking about nonlinear DSA. We use semi-analytical Blasi’s model of nonlinear DSA to obtain non-thermal spectra of both protons and electrons, starting from their quasi-thermal spectra for which we assumed the κ -distribution, a commonly observed distribution in out-of-equilibrium space plasmas. We treated more carefully than in the previous work the jump conditions at the subshock and included electron heating, resonant and, additionally, non-resonant magnetic field instabilities produced by CRs in the precursor. Also, corrections for escaping flux of protons and synchrotron losses of electrons have been made.