Radiative kinetic simulations of steady-state relativistic plasmoid magnetic reconnection

Abstract

ABSTRACT We present the results of two-dimensional particle-in-cell (PIC) simulations of relativistic magnetic reconnection (RMR) in electron–positron plasma, including the dynamical influence of the synchrotron radiation process, and integrating the observable emission signatures. The simulations are initiated with a single Harris current layer with a central gap that triggers the RMR process. We achieve a steady-state reconnection with unrestricted outflows by means of open boundary conditions. The radiative cooling efficiency is regulated by the choice of initial plasma temperature Θ. We explore different values of Θ and of the background magnetization σ0. Throughout the simulations, plasmoids are generated in the central region of the layer, and they evolve at different rates, achieving a wide range of sizes. The gaps between plasmoids are filled by smooth relativistic outflows called minijets, whose contribution to the observed radiation is very limited due to their low-particle densities. Small-sized plasmoids are rapidly accelerated; however, they have lower contributions to the observed emission, despite stronger relativistic beaming. Large-sized plasmoids are slow but produce most of the observed synchrotron emission, with major part of their radiation produced within the central cores, the density of which is enhanced by radiative cooling. Synchrotron light curves show rapid bright flares that can be identified as originating from mergers between small/fast plasmoids and large/slow targets moving in the same direction. In the high-magnetization case, the accelerated particles form a broken power-law energy distribution with a soft tail produced by particles accelerated in the minijets.