Mushroom-instability-driven Magnetic Reconnections in Collisionless Relativistic Jets

TL;DR

This paper reveals that Mushroom instability drives intermittent magnetic reconnections in collisionless relativistic jets, leading to electron acceleration and magnetic field amplification, which may explain bright emissions in active galactic nucleus jets.

Contribution

It introduces the concept of MI-driven magnetic reconnections in relativistic jets and explores their role in electron acceleration and magnetic field generation.

Findings

Magnetic reconnections are intermittently driven by Mushroom instability.

Electron acceleration correlates with the location of reconnection points.

Magnetic field amplification occurs inside the initial velocity-shear surface.

Abstract

We study the kinetic plasma dynamics in collisionless relativistic jets with velocity shear, by carrying out particle-in-cell simulations in the transverse plane of a jet. It is discovered that intermittent magnetic reconnections (MRs) are driven by Mushroom instability (MI), which is an important kinetic-scale plasma instability in the plasma shear-flows with relativistic bulk speed. We refer to this sequence of kinetic plasma phenomena as "MI-driven MR". The MI-driven MRs intermittently occur with moving the location of the reconnection points from the vicinity of the initial velocity-shear surface towards the center of the jet. As a consequence, the number density of high energy electrons, which are accelerated by MI-driven MRs, increases with time in the region inside the initial velocity-shear surface with accompanying the generation and subsequent amplification of magnetic fields by MI. The maximum Lorentz factor of electrons increases with initial bulk Lorentz factor of the jet. A possible relation of MI-driven MR to the bright synchrotron emission in jet-spine of active galactic nucleus jets is also discussed.