Berlin 2014 – wissenschaftliches Programm

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SYPA: Symposium Plasma-Astrophysik

SYPA 1: Plasma Astrophysics

SYPA 1.1: Hauptvortrag

Donnerstag, 20. März 2014, 14:00–14:30, SPA Kapelle

Cosmic Particle Acceleration — •Gaetano Zimbardo and Silvia Perri — Università della Calabria, Dipartimento di Fisica, 87036 Rende, Italy

The most popular mechanism for the acceleration of cosmic rays, which is thought to operate in supernova remnant shocks as well as at heliospheric shocks, is the diffusive shock acceleration, which is a Fermi mechanism based on normal diffusion. On the other hand, in the last few years it has been shown that the transport of plasma particles in the presence of electric and magnetic turbulence can be superdiffusive rather than normal diffusive. The term `superdiffusive' refers to the mean square displacement of particle positions growing superlinearly with time, as compared to the normal linear growth. In particular, superdiffusion is characterized by a non Gaussian statistical process called Levy random walk.

We show how diffusive shock acceleration is modified by superdiffusion, and how this yields new predictions for the cosmic ray spectral index, for the acceleration time, and for the spatial profile of energetic particles. A comparison with observations of particle acceleration at heliospheric shocks and at supernova remnant shocks is done. We discuss how superdiffusive shock acceleration allows to explain the observations of hard ion spectra at the solar wind termination shock detected by Voyager 2, of hard radio spectra due to synchrotron emission of electrons accelerated at supernova remnant shocks, and how it can help to explain the observations of `thin rims' in the X-ray synchrotron emission.