What We Learn from the Afterglow of GRB 021211

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Abstract
The behavior of the afterglow (AG) of gamma-ray bursts (GRBs) directly provides, in the cannonball (CB) model, information about the environment of their progenitor stars. The well-observed early temporal decline of the AG of GRB 021211 is precisely the one predicted in the presence of a progenitor's "wind," which resulted in a density profile ∝1/r2 around the star. The subsequent fast fading—which makes this GRB "quasi-dark"—is the one anticipated if, farther away, the interstellar density is roughly constant and relatively high. The CB model fit to the AG clearly shows the presence of an associated supernova akin to SN 1998bw and allows even for the determination of the broadband spectrum of the host galaxy. GRB 990123 and GRB 021004, whose AGs were also measured very early, are also discussed.