TAPIR Seminar
Most models of non-thermal radiation from Pulsar Wind Nebulae, gamma-ray bursts and AGN jets invoke particle
acceleration in relativistic magnetized plasmas. By means of 2D and 3D particle-in-cell simulations, we study how
the efficiency of particle acceleration in relativistic astrophysical flows depends on the plasma magnetization (ratio
"sigma" of magnetic to kinetic energy density) and the geometry of the magnetic field. We investigate both uniform
and alternating fields.
For relativistic shocks propagating in a medium with uniform fields, we find that, if sigma>0.001, only configurations
with nearly-parallel fields lead to particle acceleration. For quasi-perpendicular shocks, the level of self-generated
turbulence is insufficient to give appreciable acceleration of particles. Weakly magnetized shocks with sigma<0.001
are efficient particle accelerators, with ~1% of particles and ~10% of energy stored in a power-law tail with slope around
-2.5, whose upper energy cutoff grows as the square root of time.
In the case of strongly magnetized flows (i.e., sigma>>1) with alternating fields, we find that field dissipation mediated
by magnetic reconnection can efficiently transfer the energy from the fields to the particles, resulting in a flat power-law
tail of non-thermal electrons with slope between -1.5 and -2. Our results can place important constraints on the origin of
Ultra-High Energy Cosmic Rays, and provide physically-grounded inputs for astrophysical models of non-thermal radiation
from Pulsar Wind Nebulae, gamma-ray bursts and AGN jets.