  Recent observations suggest that long-duration gamma-ray bursts (GRBs) and
their afterglows are produced by highly relativistic jets emitted in
core-collapse explosions. The pre-explosive ambient medium provides a natural
test for the most likely progenitors of GRBs. Those stars that shed their
envelopes most readily have short jet crossing times and are more likely to
produce a GRB. We construct a simple computational scheme to explore the
expected contribution of the presupernova ejecta of single Wolf-Rayet (WR)
stars to the circumstellar environment. Using detailed stellar tracks for the
evolution of massive stars, we discuss the effects that the initial main
sequence mass, metallicity, rotation and membership in a binary system have on
the ambient medium. We extend the theory of GRB afterglows in winds to consider
the effect of the relativistic fireball propagating through the WR ejecta. We
make specific predictions for the interaction of the relativistic blast wave
with the density bumps that arise when the progenitor star rapidly loses a
large fraction of its initial mass or when the ejected wind interacts with the
external medium and decelerates. A re-brightening of the afterglow with a
spectrum redder than the typical synchrotron spectrum (as seen in GRB 970508,
GRB 980326 and GRB 000911) is predicted. We also calculate the luminosity of
the reflected echo that arises when circumstellar material Compton-scatters the
prompt radiation and examine the spectral signatures expected from the
interaction of the GRB afterglow with the ejected medium.
