Particle-in-cell simulations of shock-driven reconnection in relativistic striped winds

TL;DR

This study uses particle-in-cell simulations to show that shock-driven magnetic reconnection in relativistic striped winds efficiently converts magnetic energy into particle acceleration, producing flat power-law spectra relevant for pulsar wind nebulae and jets.

Contribution

It demonstrates that shock-driven reconnection universally accelerates particles in relativistic striped flows regardless of stripe wavelength or magnetization, with specific spectral characteristics.

Findings

Magnetic energy is fully transferred to particles at the shock.

Post-shock particle spectra develop a flat power-law tail (~-1.5 slope).

Guide magnetic fields suppress particle acceleration if stronger than alternating fields.

Abstract

By means of two- and three-dimensional particle-in-cell simulations, we investigate the process of driven magnetic reconnection at the termination shock of relativistic striped flows. In pulsar winds and in magnetar-powered relativistic jets, the flow consists of stripes of alternating magnetic field polarity, separated by current sheets of hot plasma. At the wind termination shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength "lambda" or the wind magnetization "sigma" (in the regime sigma>>1 of magnetically-dominated flows), shock-driven reconnection transfers all the magnetic energy of alternating fields to the particles, whose average Lorentz factor increases by a factor of sigma with respect to the pre-shock value. In the limit lambda/(r_L*sigma)>>1, where r_L is the relativistic Larmor radius in the wind, the post-shock particle spectrum approaches a flat power-law tail with slope around -1.5, populated by particles accelerated by the reconnection electric field. The presence of a current-aligned "guide" magnetic field suppresses the acceleration of particles only when the guide field is stronger than the alternating component. Our findings place important constraints on the models of non-thermal radiation from Pulsar Wind Nebulae and relativistic jets.