Speaker
Description
Astrophysical shocks are considered to be one of the main sources of cosmic rays in the universe. Long-term observations of gamma-ray burst (GRB) afterglows, the recent detection of >100 TeV gamma-rays from microquasars, and the discovery of fast blue optical transients (FBOTs) motivate us to investigate transrelativistic shocks, which are underexplored, in terms of microphysics, compared to ultrarelativistic shocks. Using particle-in-cell (PIC) simulations, we show that magnetic field amplification and particle acceleration characteristics depend strongly on shock velocity and on upstream magnetic field strength. Shocks with a relatively strong upstream magnetic field and a slow velocity accelerate ions efficiently, but the fraction of energy going into nonthermal electrons is small. On the other hand, shocks with a relatively weak magnetic field and a fast velocity accelerate ions less efficiently while converting significantly more energy into nonthermal electrons. We apply our PIC simulation results to the maximum energy of gamma-rays and variability in X-ray emission, both in terms of brightness and thermal/nonthermal origin.
