Rapid high-energy emission variability in relativistic pair plasma reconnection

Abstract

We report on the first study of energetic particles and radiation angular distributions generated in relativistic collisionless pair plasma reconnection, using 2.5-dimensional particle-incell simulations. We have discovered that the energetic particles are focused within a small solid angle, and bunched into compact regions inside magnetic islands. In addition, we find that the synchrotron radiation emitted by these particles, as seen by an external observer, is tightly beamed and variable on time scales much shorter than the light-crossing time of the system. This energy dependent "kinetic beaming" differs fundamentally from the achromatic Doppler beaming usually ascribed to relativistic jets. Our findings can account for the puzzling discoveries of bright, short flares seen in high-energy gamma rays, especially from the Crab Nebula and from blazars.