Abstract

Contributed Talk - Splinter NonThermalAccel   (MW-1250)

Ion and electron acceleration in strongly magnetized mildly relativistic shocks

G. Torralba Paz, J. Niemiec, M. Hoshino, T. Amano and S. Matsukiyo
Max Planck Institute for Plasma Physics, Institute of Nuclear Physics Polish Academy of Sciences, University of Tokyo, Kyushu University

We demonstrate that magnetized mildly relativistic shocks may be efficient particle accelerators capable of accounting for the intense X-ray and gamma-ray emission observed in jets of active galactic nuclei (AGN). Using the particle-in-cell (PIC) method, we simulate shocks propagating through magnetized electron-ion plasmas for two subluminal magnetic field configurations: an oblique configuration with the magnetic field oriented just below the critical angle, and a quasi-parallel configuration. The results show notable difference between both simulations despite a slight difference in the obliquity angle. In the oblique configuration, electrons stream primarily along magnetic field lines. A portion of these become efficiently trapped by the cross-shock electrostatic potential. Rather than escaping downstream, these particles oscillate within the potential structure, where they gain energy from the motional electric field and the shock potential itself, reaching highly relativistic energies. Ions are similarly trapped, albeit within electrostatic potential wells, and achieve comparable maximum kinetic energies. A fraction of these energized ions subsequently escape into the upstream region, where they undergo shock surfing acceleration along the shock front. In contrast, the quasi-parallel shock self-consistently generates elliptically polarized whistler waves that propagate upstream. A fraction of downstream ions escape from the non-stationary downstream region towards the upstream, where they become trapped by longitudinal electric fields produced through the oblique propagation of these whistler waves, leading to efficient heating to relativistic temperatures. The resulting upstream plasma distribution is further modified by the development of the modified two-stream instability (MTSI) and the parametric decay instability (PDI), both of which contribute to the overall energy dissipation and particle heating.