  The diverse and complex light curves of gamma-ray bursts (GRBs) remain an
outstanding astrophysical mystery. Here we report the results of
2-1/2-dimensional particle-in-cell (PIC) simulations of the relativistic
expansion of magnetized electron-positron plasmas. When the simulation is
carried to >150 light-crossing time of the initial plasma, the plasma pulse
reproduces many of the GRB features. Remarkably, the plasma pulse bifurcates
repeatedly, leading to a complex, multi-peak structure at late times,
resembling GRB profiles.
