  Likely progenitors for the GRBs (gamma-ray bursts) are the mergers of compact
objects or the explosions of massive stars. These two cases have distinctive
environments for the GRB afterglow: the compact object explosions occur in the
ISM (interstellar medium) and those of massive stars occur in the preburst
stellar wind. We calculate the expected afterglow for a burst in a Wolf-Rayet
star wind and compare the results to those for constant, interstellar density.
The optical afterglow for the wind case is generally expected to decline more
steeply than in the constant density case, but this effect may be masked by
variations in electron spectral index, and the two cases have the same
evolution in the cooling regime. Observations of the concurrent radio and
optical/X-ray evolution are especially useful for distinguishing between the
two cases. The different rates of decline of the optical and X-ray afterglows
of GRB 990123 suggest constant density interaction for this case. We have
previously found strong evidence for wind interaction in SN 1998bw/GRB 980425
and here present a wind model for GRB 980519. We thus suggest that there are
both wind type GRB afterglows with massive star progenitors and ISM type
afterglows with compact binary star progenitors. The wind type bursts are
likely to be accompanied by a supernova, but not the ISM type.
