Shown in Figures 2(a) and (b) are the z-component of the electric field, Ez, and y-component of the magnetic field, By, respectively. Panels 2(c)–(e) show the transversally averaged (in the yz-plane) electric and magnetic field components, 





. The energy distribution (total of jet+ambient) and average energy along the x-direction for electron and ion species are shown in Figures 2(f)–(i). All panels are at t∗ = 500. Where high-speed jet particles interact with the ambient medium (behind the RS at x∗ ≤ 340) or scattered ambient particles blend with the upstream ambient (in front of the FS at 430 ≤ x∗), particles distribution becomes strongly anisotropic. Anisotropies result in the Weibel instability which generates current filaments in these regions with currents in the x-direction. According to Ampere’s law, these current filaments are encircled by transverse magnetic fields, and we see that 





 in Figure 2(c). The transverse electric fields are related to the magnetic fields via 





 where 





 is the velocity of the electron (ion) carrier. The carriers move roughly at the speed of light in the x-direction, 





. Therefore, the transverse electric field components are Ey = Bz, and Ez = −By, as are observed in the simulation results for 





 (Figures 2(a)–(e)). Additionally, there is a longitudinal ambipolar electric field within the RS transition region, 140 ≤ x∗ ≤ 340 for t∗ = 500 (Figure 2(c)). This electric field is generated by the density gradient and different mobilities of electrons and ions (Forslund & Shonk 1970; Forslund & Freidberg 1971; Hoshino 2001; Choi et al. 2014). The magnetic fields act to isotropize the momentum distribution, while the electric fields function to thermalize, and accelerate the particles afterwards. In Figures 2(f)–(i), the shocked region lies between x∗ = 340 and x∗ = 430. Within the RS transition region (140 ≤ x∗ ≤ 340) jet electrons are trapped by the ambipolar electric field and effectively accelerated up to γe = 200 by the transverse electric fields (Figures 2(f) and (g)). A tenuous population of these electrons convect upstream due to reflection by the magnetic fields in the shocked region (ellipse in Figure 2(f)). On the other hand, jet ions are slowed in the RS transition region (140 ≤ x∗ ≤ 340) by 40% from the initial Lorentz factor γi = 10, due to the effect of the ambipolar electric field. In the shocked region, jet electrons have been fully thermalized and are well merged with the thermalized ambient electrons. Thus, only a single electron population is present in the hot shocked region (Figure 2(f)). On the other hand, the kinetic energy of jet ions is transferred to the heating of ambient particles by means of the electromagnetic fields generated by the ion Weibel instability (Figure 2(h)). Full thermalization of the two ion populations (jet and ambient) has not yet occured (demands a longer simulation time), i.e., the two populations are distinguishable in Figure 2(h). Electrons located in the FS transition region (430 ≤ x∗ ≤ 500), predominantly ambient electrons, also undergo the Weibel instability and are thermalized by the jet upstream kinetic energy. In this region, penetrating jet ions interact with ambient particles and are slowed down gradually by 50% from the jet front Lorentz factor γi = 10 to a minimum value of γi = 5 (Figures 2(h) and (i)).
Citation: Choi et al. 2014
Citation function: Uses