Nonlinear Monte Carlo model of superdiffusive shock acceleration with magnetic field amplification

Compound electron acceleration at planetary foreshocks

Shock waves, the interface of supersonic and subsonic plasma flows, are the primary region for charged particle acceleration in multiple space plasma systems, including Earth's bow shock, which is readily accessible for in-situ measurements. Spacecraft frequently observe relativistic electron populations within this region, characterized by energy levels surpassing those of solar wind electrons by a factor of 10,000 or more. However, mechanisms of such strong acceleration remain elusive. Here we use observations of electrons with energies up to 200 kiloelectron volts and a data-constrained model to reproduce the observed power-law electron spectrum and demonstrate that the acceleration by more than 4 orders of magnitude is a compound process including a complex, multi-step interaction between more commonly known mechanisms and resonant scattering by several distinct plasma wave modes. The proposed model of electron acceleration addresses a decades-long issue of the generation of energetic (and relativistic) electrons at planetary plasma shocks. This work may further guide numerical simulations of even more effective electron acceleration in astrophysical shocks.

Ultra-high energy cosmic rays and the strongest AGN flares

We perform an observational test of the hypothesis that ultra-high energy cosmic rays (E > 1020 eV) are accelerated in giant flares of active galactic nuclei (AGN). We use the observations of Fermi LAT during the first 7.4 years of the mission. We select highly variable AGNs with the redshift z ≤ 0:3 and use an empirical relation between the bolometric luminosity and the jet kinetic power in order to find the local kinetic emissivity of strong AGN flares: L ~ 1:1 × 1045erg Mpc-3 yr-1. This is approximately one order of magnitude larger than the UHECR emissivity estimated from the data of Pierre Auger and Telescope Array observatories which makes the whole scenarion feasible provided the acceleration spectrum is sufficiently hard and/or narrow.