A PIC Simulation Study for Electron Preacceleration at Weak Quasi-Perpendicular Galaxy Cluster Shocks

  • Ha, Ji-Hoon (Department of Physics, School of Natural Sciences UNIST) ;
  • Kim, Sunjung (Department of Physics, School of Natural Sciences UNIST) ;
  • Ryu, Dongsu (Department of Physics, School of Natural Sciences UNIST) ;
  • Kang, Hyesung (Department of Earth Sciences, Pusan National University)
  • Published : 2021.04.13

Abstract

In the outskirts of galaxy clusters, weak shocks with Ms < ~3 appear as radio relics where the synchrotron radiation is emitted from cosmic-ray (CR) electrons. To understand the production of CR electrons through the so-called diffusive shock acceleration (DSA), the electron injection into the DSA process at shocks in the hot intracluster medium (ICM) has to be described. However, the injection remains as an unsolved, outstanding problem. To explore this problem, 2D Particle-in-Cell (PIC) simulations were performed. In this talk, we present the electron preacceleration mechanism mediated by multi-scale plasma waves in the shock transition zone. In particular, we find that the electron preacceleration is effective only in the supercritical shocks, which have the sonic Mach number Ms > Mcrit ≈ 2.3 in the high-beta (β~100) plasma of the ICM, because the Alfven ion cyclotron instability operates and hence multi-scale plasma waves are induced only in such supercritical shocks. Our findings will help to understand the nature of radio relics in galaxy clusters.

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