  We present Follow-Up Network for Gamma-Ray Bursts (FUN GRB) Collaboration
observations of the optical afterglow of GRB 021211 made between 143 seconds
and 102 days after the burst. Our unique data set includes the earliest
filtered detections and color information for an afterglow in the pre-Swift
era. We find that the afterglow is best described by (1) propagation through a
wind-swept medium, (2) a cooling break that is blueward of the observed optical
frequencies, and (3) a hard electron energy distribution. However, superimposed
on this "standard model" behavior we find significant chromatic variations
within the first few hours after the burst. We consider possible reasons for
these variations, including the possibility that they are due to a dust echo.
Finally, we constrain physical parameters that describe the afterglow and
surrounding medium for a variety of scenarios and find that GRB 021211's
afterglow is faint for a combination of 3-4 reasons: (1) a low fraction of
energy in relativistic electrons, (2) a low density for the wind-swept medium,
implying either a low mass-loss rate and/or a high wind velocity for the
progenitor, (3) a wide opening/viewing angle for the jet, and possibly (4)
moderate source frame extinction. The jet appears to be significantly far from
equipartition and magnetically dominated. More extreme versions of this might
explain the darkness of many afterglows in the Swift era.

Astrophysics