Structure of a strong supernova shock wave and rapid electron acceleration confined in its transition region

A new rapid energization process within a supernova shock transition region (STR) is reported by utilizing numerical simulation. Although the scale of a STR as a main dissipation region is only several hundreds of thousands of kilometers, several interesting structures are found relating to the generation of a root of the energetic particles. The nonlinear evolution of plasma instabilities leads to a dynamical change in the ion phase space distribution, which associates with change in the field properties. As a result, different types of large-amplitude field structures appear. One is the leading wave packet, and another is a series of magnetic solitary humps. Each field structure has a microscopic scale (that is, the ion inertia length). Through the multiple nonlinear scattering between these large-amplitude field structures, electrons are accelerated directly. Within a STR, quick thermalization realizes energy equipartition between the ion and electron; hot electrons play an important role in keeping these large-amplitude field structures on the ion-acoustic mode. The hot electron shows non-Maxwellian distribution and could be the seed of further nonthermal population. The 'shock system', where fresh incoming and reflected ions are supplied constantly, play an essential role in our result. With a perpendicular shock geometry, the maximum energy of the electron is estimated by equating a width of the STR to a length of the Larmor radius of the energetic electron. Under some realistic condition of MA=170 and ωpe/Ωce=120, maximum energy is estimated to be ∼10 MeV at an instant only within the STR.