The CCD Johnson BV and Cousins RI photometric magnitudes are determined for 20 stars in the field of GRB 000926 .
They are used to calibrate the present R as well as published BVRI photometric magnitudes of the GRB 000926 afterglow .
Optical light curves of the afterglow emission are obtained in B and R passbands .
They show a steepening of the flux decay as expected of an anisotropic fireball losing collimation with the fall of the bulk Lorentz factor .
We derive the early and late time flux decay constants as 1.4 \pm 0.1 and 2.6 \pm 0.06 respectively .
Steepening in the flux decay seems to have started around 1.7 days after the burst .
Negligible Galactic but relatively large intrinsic extinction amounting E ( B - V ) = 0.03 and 0.36 \pm 0.02 mag respectively are derived in the direction of GRB 000926 .
The value of the spectral index in the X-ray–optical–near-infrared region is \sim - 0.9 .
The determination of the redshift z = 2.0369 indicates a cosmological origin of the burst at a luminosity distance of 16.6 Gpc .
The observed fluence in the energy range 20–100 keV indicates , if isotropic , the release of \geq 10 ^ { 53 } ergs of energy .
Attributing the observed break in the light curve at 1.7 days to the onset of sideways expansion of a jet-like ejecta , we infer an initial jet opening angle of \sim 0.14 radian .
This indicates a large anisotropy in the original emission and the amount of released energy is reduced by a factor of \sim 100 relative to the isotropic value , which can be understood in terms of the currently popular stellar death models .