Speaker
Description
Pulsar wind nebulae (PWNe) are among the most prominent non-thermal sources in the high-energy sky, emitting radiation from radio to gamma-ray energies. These observations imply extremely efficient acceleration of particles to ultra-relativistic energies, yet the physical mechanism responsible for this energization remains unknown. The termination shock of the relativistic pulsar wind is widely regarded as a promising site of particle acceleration. However, the production of a non-thermal particle population remains unexplained, since diffusive shock acceleration is not expected to operate efficiently at relativistic quasi-perpendicular shocks, where the upstream magnetic field lies predominantly in the shock plane. I will present a possible acceleration process in relativistic quasi-perpendicular electron-positron shocks relevant to PWNe. The shock launches a strong electromagnetic precursor into the upstream plasma, which is initially threaded by a uniform background magnetic field. I will show that this precursor becomes unstable to filamentation, producing radiation filaments aligned with the shock normal and with transverse scales of a few plasma skin depths. In the shock frame, the upstream flow is significantly decelerated inside these filaments, generating relativistic shear flows with strong kinetic-scale velocity gradients. These gradients distort the background magnetic field and induce a magnetic-field component parallel to the shock normal that reverses across neighboring filaments. Such a configuration may trigger magnetic reconnection upstream of the shock and enable particle energization before the plasma reaches the shock front. These results point to a new pathway for non-thermal particle acceleration in relativistic magnetized pair shocks.
