What We Learn from the Afterglow of GRB 021211

The behaviour of the afterglow (AG) of gamma-ray bursts (GRBs) directlyprovides, in the cannonball (CB) model, information about the environment oftheir progenitor stars. The well observed early temporal decline of the AG ofGRB 021211 is precisely the one predicted in the presence of a progenitor's``wind'' which resulted in a density profile $\propto 1/r^2$ around the star.The subsequent fast fading --which makes this GRB ``quasi-dark''-- is the oneanticipated if, further away, the interstellar density is roughly constant andrelatively high. The CB-model fit to the AG clearly shows the presence of anassociated supernova akin to SN1998bw, and allows even for the determination ofthe broad-band spectrum of the host galaxy. GRB 990123 and GRB 021004, whoseAGs were also measured very early, are also discussed.Comment: Figures 4 and 5 replaced by correct figure