We present early-time optical photometry and spectroscopy of the optical afterglow of the gamma-ray burst ( catalog GRB~011211 ) .
The spectrum of the optical afterglow contains several narrow metal lines which are consistent with the burst occurring at a redshift of 2.140 \pm 0.001 .
The optical afterglow decays as a power law with a slope of \alpha = 0.83 \pm 0.04 for the first \approx 2 days after the burst at which time there is evidence for a break .
The slope after the break is \geq 1.4 .
There is evidence for rapid variations in the R -band light approximately 0.5 days after the burst .
These variations suggest that there are density fluctuations near the gamma-ray burst on spatial scales of approximately 40–125 AU .
The magnitude of the break in the light curve , the spectral slope , and the rate of decay in the optical , suggest that the burst expanded into an ambient medium that is homogeneous on large scales .
We estimate that the local particle density is between approximately 0.1 and 10 cm ^ { -3 } and that the total gamma-ray energy in the burst was 1.2 – 1.9 \times 10 ^ { 50 } erg .
This energy is smaller than , but consistent with , the “ standard ” value of ( 5 \pm 2 ) \times 10 ^ { 50 } erg .
Comparing the observed color of the optical afterglow with predictions of the standard beaming model suggests that the rest-frame V -band extinction in the host galaxy is \lesssim 0.03 mag .