| Gamma-ray bursts (GRBs) have been a challenge for astronomers ever since their serendipitous discovery by the Vela satellites in the late 1960s and early 1970s. In this thesis, we explore plausible observational diagnostics of the surroundings of GRBs. First, we analyze high-resolution grating spectroscopy of GRB 020405 and consider the physical properties of GRB environments including the density and extent of their X-ray emitting region. Although the absence of discrete features in these observations does not unambiguously test for a connection between GRBs and nucleosynthesis, it emphasizes the need for future high-resolution X-ray spectroscopy if emission lines such as those reported in other GRB afterglows were to be detected again. Complementing these findings, we examine the feasibility of probing UV and optical absorption lines that are physically associated with the GRB progenitor. Perhaps the most dramatic conclusion is that material intrinsic to the GRB progenitor should exhibit time-dependent absorption features due to the photoionization of the surrounding medium. Unfortunately, no absorption systems have been identified as truly intrinsic at the time of this writing. However, the presence of multiple absorption components in the spectra of GRB afterglows, separated by velocities of up to 3,155 km s-1, could be attributed to circumstellar material from the progenitor that has been radiatively accelerated by the GRB radiation. Lastly, we consider broadband emission models and prominent re-brightenings in the GRB 021004 and GRB 030329 afterglows. Both cases are consistent with surroundings shaped by the clumpy winds expected around massive-star GRB progenitors. |
