||Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields
||444, 5th International Conference of Numerical Modeling of Space Plasma Flows (ASTRONUM 2010)
||Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.
||Using our new 3-D relativistic particle-in-cell (PIC) code, we investigated long-term particle
acceleration associated with a relativistic electron-positron jet
propagating in an unmagnetized ambient electron-positron plasma. The
simulations were performed using a much longer simulation system
than our previous simulations in order to investigate the full
nonlinear stage of the Weibel instability and its particle
acceleration mechanism. Cold jet electrons are thermalized and ambient
electrons are accelerated in the resulting shocks. Acceleration of
ambient electrons leads to a maximum ambient electron density three
times larger than the original value as predicted by the hydrodynamic compression.
Behind the bow shock, in the jet
shock, strong electromagnetic fields are generated. These fields may
lead to time dependent afterglow emission.
In order to go beyond the standard synchrotron
model used in astrophysical objects we have used PIC simulations and calculated radiation
based on the first principles. We calculated radiation from
electrons propagating in a uniform parallel magnetic field to verify the
technique. We also used the technique to calculate emission from
electrons based on simulations with a small system. We obtained spectra
which are consistent with those generated from electrons propagating
in turbulent magnetic fields. This turbulent magnetic field
is similar to the magnetic field generated at an early nonlinear stage
of the Weibel instability. A fully developed shock within a larger system
may generate a jitter/synchrotron spectrum.