2:15 PM - 2:30 PM
[PEM17-08] Electron mirror reflection at non-relativistic, high Mach number oblique shocks
Keywords:shock, electron acceleration, PIC simulation
Electron cosmic ray acceleration at supernova remnant (SNR) shocks is one of the outstanding issues in astrophysics due to the difficulty of electrons being subject to the diffusive shock acceleration. The so-called electron injection problem is the central part of our problem, which is tackled by ab-initio particle-in-cell (PIC) simulations. Recently, the injection has been described in PIC simulations of quasi-perpendicular high Mach number shocks (Xu et al., 2020; Kumar & Reville, 2021; Morris et al., 2022; Bohdan et al., 2022). In oblique shocks, electrons are mirror reflected from the shock front after undergoing a preheating process through the Buneman instability. Due to the quasi-perpendicular geometry, the reflected particles have relativistic energies and sufficient energy density to excite electromagnetic and electrostatic waves in the upstream region. These excited waves are crucial for scattering escaping particles and injecting them into the cyclic Fermi acceleration process.
We study such electron reflections for different shock speeds using a newly developed PIC simulation code adapted to the Fugaku supercomputer. With our two-dimensional (2D) load-balanced simulation code, we could follow the long-term evolution and thus track the escaping electrons in the upstream region. With a shock angle of 70 degrees, we find that the Buneman instability is excited with large amplitudes at the leading edge of the foot for shock speeds down to 10% of the speed of light. Although the energy gain of the particles from the Buneman instability is limited in such a truly non-relativistic regime, it plays a crucial role in pushing the particle's pitch angle closer to 90 degrees. The resulting high-pitch angle particles are subject to further mirror reflection at the shock front and thus have an efficient reflection rate even in the high Mach number shocks. In this presentation, we describe the results of 2D PIC simulations, focusing on electron reflection and its implications for realistic SNR shock speeds.
We study such electron reflections for different shock speeds using a newly developed PIC simulation code adapted to the Fugaku supercomputer. With our two-dimensional (2D) load-balanced simulation code, we could follow the long-term evolution and thus track the escaping electrons in the upstream region. With a shock angle of 70 degrees, we find that the Buneman instability is excited with large amplitudes at the leading edge of the foot for shock speeds down to 10% of the speed of light. Although the energy gain of the particles from the Buneman instability is limited in such a truly non-relativistic regime, it plays a crucial role in pushing the particle's pitch angle closer to 90 degrees. The resulting high-pitch angle particles are subject to further mirror reflection at the shock front and thus have an efficient reflection rate even in the high Mach number shocks. In this presentation, we describe the results of 2D PIC simulations, focusing on electron reflection and its implications for realistic SNR shock speeds.