Theoretical implications of the gamma-ray burst-supernova connection

Although observations of circumstellar shock interactions around supernovae are generally consistent with a p proportional to r(-2) wind surrounding the progenitor star, this is not true for GRB (gamma-ray burst) afterglows. However, GRB 991208 and GRB 000301C may be consistent with wind interaction if the injection particle spectrum is a broken power law. Circumstellar dust echos can place constraints on supernova and GRB progenitors, but have been clearly observed only around SN 1987A. Excess emission observed in two GRB afterglows is more likely to have a supernova origin. An interstellar dust echo, causing the light curve to flatten out, is a possibility for GRB afterglows, but is not likely to be observable.