From Turbulence to Reconnection to Particle Acceleration: Connecting the Dots

by Luca Comisso (Columbia University)

Tuesday 20 Oct 2020, 15:00 → 16:00 Europe/Stockholm

https://stockholmuniversity.zoom.us/j/940229961

Comisso_20-Oct-2020.mp4

Magnetic reconnection and magnetized turbulence are often invoked to explain the generation of nonthermal particles inferred in a wide variety of astrophysical settings. By means of fully-kinetic particle-in-cell simulations of magnetically dominated pair plasmas, we investigate the interplay between magnetic reconnection and turbulence in generating nonthermal particle distributions with a power-law high energy range. Plasmoid-mediated reconnection, which self-consistently occurs in the turbulent plasma, controls the initial stage of particle acceleration. Then, particles are further accelerated by stochastic scattering off large-scale turbulent fluctuations. This two-stage particle acceleration process leads to strongly anisotropic particle distributions. At modest particle Lorentz factors, the particle velocity is preferentially aligned with the local magnetic field. On the other hand, the highest-energy particles are preferentially oriented in the plane perpendicular to the magnetic field. This energy-dependent anisotropy leads to a synchrotron spectral flux that is much harder than for isotropic particles. These findings have implications for understanding the origin of nonthermal particles and explain the hard synchrotron spectra of astrophysical nonthermal sources.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.255101
https://iopscience.iop.org/article/10.3847/1538-4357/ab4c33
https://iopscience.iop.org/article/10.3847/2041-8213/ab93dc