2003ApJ...586L...9L

The Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory observed gamma-ray burst GRB 021211 starting 105 s after the burst, among the earliest observations of an optical afterglow to date. Our well-sampled light curve, consisting of 18 points in the first 10 minutes and a total of 28 useful observations in the first 2.5 hr after the GRB, directly shows for the first time a break at t~10 minutes. The light curve can be represented as a sum of two components with power-law decay indices of -1.82±0.02 and -0.82±0.11. We hypothesize that the data before the break were dominated by emission from the reverse shock, as was previously suggested for GRB 990123. Our data suggest that either GRB 021211 underwent a dramatic color change at early times or there are small-scale variations superposed on the power-law decay of the reverse-shock emission. The faintness of GRB 021211, coupled with the fast decline typical of optical afterglows, suggests that some of the ``dark bursts'' were not detected because optical observations commenced too late after the GRB.