Cosmic-ray acceleration at perpendicular shocks

摘要

Diffusive shock acceleration (DSA) in supernova remnants is the dominant paradigm for the acceleration of cosmic rays in the Galaxy. However, the maximum possible energy to which parallel shocks can accelerate protons in these objects is only roughly 1PeV [1], in tension with the observed cosmic ray spectrum. Perpendicular shocks present a possible alternative [4], and are expected to predominate if the supernova progenitor is a rotating, massive star with a powerful wind [2]. However, stochastic acceleration in this situation is complicated, because the underlying transport process is not necessarily diffusive, in which case the standard results concerning particle spectra and acceleration rates lose their validity [6]. This paper presents a new approximate, analytical approach to the test particle problem at perpendicular shocks, using an expansion in eigenfunctions of the pitch-angle and phase dependent scattering operator. An explicit expression for the spectral index of accelerated particles is found and compared with the results of Monte-Carlo simulations. Full details can be found in [7].