GRB 021211 as a Faint Analog of GRB 990123: Exploring the Similarities and Differences in the Optical Afterglows

We present B, V, Rc, J, H, and Ks photometry of the optical afterglow of thegamma-ray burst GRB 021211 taken at the Magellan, MMT, and WIYN observatoriesbetween 0.7 and 50 days after the burst. We find an intrinsic spectral slope atoptical and near-infrared wavelengths of 0.69 +/- 0.14 at 0.87 days. Theoptical decay during the first day is almost identical to that of GRB 990123except that GRB 021211's optical afterglow was intrinsically approximately 38times fainter, and the transition from the reverse shock to the forward shockmay have occurred earlier than it did for GRB 990123. We find no evidence for ajet break or the cooling break passing through optical frequencies during thefirst day after the burst. There is weak evidence for a break in the J-banddecay between 0.89 and 1.87 days which may be due to a jet. The optical andinfrared data are consistent with a relativistic fireball where the shockedelectrons are in the slow cooling regime and the electron index is 2.3 +/- 0.1.The forward shock appears to have been expanding in a homogeneous ambientmedium during the first day after the burst. Our analysis suggests that the jetof GRB 021211 may have a small opening angle and that the total gamma-rayenergy is likely to be much less than the canonical value of 1.33E+51 erg. Ifthis is the case then it is possible that most of the energy of the burst is inanother form such as a frozen magnetic field, supernova ejecta, or a second jetcomponent. The host galaxy of GRB 021211 is subluminous and has a starformation rate of at least one Solar mass per year.Comment: 24 pages, 4 figures, LaTex using AASTeX v5.2, to the Nov 2004 Astronomical Journal. Some minor changes have been made to the paper in accordance with the referee's repor