| Gamma-ray bursts (GRBs) and their afterglows are most naturally described by the relativistic “fireball” model in which various internal and external shocks play essential roles. We study the interaction between the relativistic GRB shocks and the surrounding medium under different circumstances. The observational implications could be used to probe the gaseous environments of GRB sources.; This research project consists of four studies. (1) We study the variability of GRB afterglows due to interstellar turbulence. We calculate the amplitude of flux fluctuations in the afterglow light curves for different length scales of the inhomogeneities in the surrounding medium. We predict that hourly monitoring of optical afterglows might reveal fractional flux fluctuations at the level of a few percent. (2) We study the emission from bow shocks of collimated GRB jets. This emission may dominate over the direct emission from the jet for lines of sight that are outside the jet cone. We find that for typical GRB parameters, the bow shock synchrotron emission from a jet of half-angle ∼5° is visible out to tens of Mpc in the radio and hundreds of Mpc in the X-ray. (3) We study the stability of a relativistic forward/reverse-shock system that forms when the fireball of a GRB impacts on the surrounding medium. We find the shock system to be stable for either a uniform or a wind (r−2) external density profile. However, perturbations in the double-shock system could induce damped oscillatory fluctuations in the observed flux on short timescales during the early phase of an afterglow. These fluctuations are detectable if the initial perturbations are sufficiently large. (4) We study the stability of the self-similar solutions for an accelerating relativistic blast wave in a steep density profile of the external medium (ρ ∝ r−k, k > 4.134). These accelerating solutions apply, for example, to the breakout of a GRB outflow from the boundary of a massive star in the popular collapsar model. We find that short wavelength perturbations may grow but only by a modest factor 10. |
