Effects of circumstellar shells on long gamma-ray burst afterglow dynamics

Gamma-ray bursts (GRBs) are the most energetic electromagnetic phenomena in the known universe. However, much remains unknown about the specific mechanism driving their long-term evolution. Current models frequently focus on complex behavior involving the GRB progenitor but assume simple circumstellar environments. Many long GRBs, however, show late-time optical and x-ray flares which may indicate a much richer environment. Relativistic hydrodynamics simulations are used to evolve a family of initial data for a relativistic blast wave colliding with a circumstellar shell similar to what an aging star expelling the outer layers of its atmosphere might generate. The possibility that this interaction contributes to late-time variability is tested. Under favorable circumstances, the results indicate the possibility of late-time thermal flares in the optical or x-ray range. Preliminary results on synchrotron radiation from the reverse shock will also be presented, as well as how these results compare to existing observations.