Stochastic reacceleration of relativistic electrons by turbulent reconnection: a mechanism for cluster-scale radio emission?

• Published in: Monthly notices of the Royal Astronomical Society 2016-05, Vol.458 (3), p.2584-2595
• Main Authors: Brunetti, G., Lazarian, A.
• Format: Article
• Language: English
• Subjects: Acceleration; Astronomy; Computational fluid dynamics; Diffusion; Electrons; Fluid flow; Magnetohydrodynamic turbulence; Radio emission; Relativistic particles; Star & galaxy formation; Turbulence; Turbulent flow
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw496

In this paper, we investigate a situation where relativistic particles are reaccelerated diffusing across regions of reconnection and magnetic dynamo in super-Alfvenic, incompressible large-scale turbulence. We present an exploratory study of this mechanism in the intracluster medium (ICM). In view of large-scale turbulence in the ICM, we adopt a reconnection scheme that is based on turbulent reconnection and magnetohydrodynamics (MHD) turbulence. In this case, particles are accelerated and decelerated in a systematic way in reconnecting and magnetic-dynamo regions, respectively, and on longer time-scales undergo a stochastic process diffusing across these sites (similar to second-order Fermi). Our study extends on larger scales numerical studies that focused on the acceleration in and around turbulent reconnecting regions. We suggest that this mechanism may play a role in the reacceleration of relativistic electrons in galaxy clusters providing a new physical scenario to explain the origin of cluster-scale diffuse radio emission. Indeed differently from current turbulent reacceleration models proposed for example for radio haloes, this mechanism is based on the effect of large-scale incompressible and super-Alfvenic turbulence. In this new model, turbulence governs the interaction between relativistic particles and magnetic field lines that diffuse, reconnect and are stretched in the turbulent ICM.