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Gamma ray bursts (GRBs) are thought to originate from highly relativistic jets. The fireball model predicts internal shocks in the jets, causing magnetic field to be amplified and particles to be accelerated. We model the effects of an asymmetric density configuration for an internal plasma collision in a quasi-parallel magnetic field. We measured electron acceleration and found that a tenuous population of electrons is accelerated to Lorentz factors of \sim 300 - close to energy equipartition with ions. We found that the filaments did not remain static, but were deflected by the Lorentz force and rolled up into small vortices, which themselves merge to form a larger current vortex., Comment: 4 pages, 5 figures; Procceedings of the workshop "High Energy Phenomena in Relativistic Outflows III" (HEPRO III), Barcelona, June 27 - July 1, 2011

A gamma-ray burst (GRB) is triggered by a stellar implosion and the subsequent ejection of an ultrarelativistic jet. The prompt emissions are attributed to mildly relativistic collisions of plasma clouds within this jet. The resulting internal shocks are instrumental in the generation of the magnetic fields and the energetic electrons, which excite the observed electromagnetic emissions. We use particle-in-cell (PIC) simulations to examine such a shock. The colliding hot magnetized plasma clouds have densities that differ by a factor of 10. Current channels form rapidly in the 3D simulation, which resemble those in a Hammer–Rostoker equilibrium, are observed also in the 2D simulation. The 2D simulation also shows the formation of a shock, which is mediated by a strong electromagnetic wave, and the energy equipartition between electrons and ions.