Institute for Advanced Study Informal Astrophysics Seminar

One century after the pioneering discovery of cosmic rays by V. Hess, the present generation of X- and gamma-ray telescopes is finally unravelling the origin of extraterrestrial particles with energies up to 10^8 GeV, which are thought to be accelerated in the forward shocks of Galactic supernova remnants (SNRs). I discuss the present theoretical understanding of particle acceleration at non-relativistic, collisionless shocks, addressing with both analytical and numerical kinetic techniques the crucial interplay between accelerated ions and magnetic turbulence. In SNRs, in fact, magnetic fields turn out to be factors of 10-100 larger than in the interstellar medium because of plasma instabilities triggered by energetic particles. In particular, I show 2D and 3D hybrid (fluid electrons - kinetic ions) simulations, discussing the efficiency of Fermi acceleration and the role of the cosmic-ray-induced instabilities in amplifying the magnetic field up to the levels inferred at the blast waves of young Galactic SNRs. Finally, I outline the observational counterparts of such a theory in terms of multi-wavelength emission, with a special attention to SN1006 and Tycho, arguably the best SNRs where to test particle acceleration and magnetic field amplification.