Optical afterglow observations of gamma-ray bursts

Optical afterglows of GRBs provide vital information about the nature of the progenitors and the energetics. Observed achromatic steepening in several optical afterglow light-curves show evidence for the presence of the jet-break, constraining the total output energy. Intrinsic values of spectral indices also indicate towards considerable host galaxy extinction in a few GRBs. Superposed variability in the observed afterglow light curves indicate the nature of progenitors as massive stars. Recent optical afterglow observations of GRB 030329/SN 2003dh strengthen the SN-GRB connection. Multi-band modeling of afterglows are also able to constrain the radiation mechanisms involved and the environments of GRBs.