Numerical simulations of local shock reformation and ion acceleration in supernova remnants

The identification of preacceleration mechanisms for cosmic rays in supernova remnant shocks is an outstanding problem in astrophysics. Recent particle-in-cell (PIC) shock simulations have shown that the inclusion of the full electron kinetics yields non-time-stationary solutions, in contrast to previous hybrid (kinetic ions, fluid electrons) simulations. Here, by running a PIC code at high phase space resolution, we identify a new ion acceleration mechanism associated with the time dependence of the shock. From simple scaling arguments, these results suggest that for realistic parameters at supernova remnant shocks, such as an inflow speed of around 2.5 x 10(7) m s(-1), an accelerated ion population is created at energies of order 10-20 MeV. These simulations indicate the importance of capturing the full self-consistent plasma dynamics in order to study preacceleration.