Ram Sagar and Kuntal Misra
Aryabhatta Research Institute of Observational
Sciences, Manora Peak, Nainital 263 129, India
Abstract. Optical observations of GRB afterglows provide information
about
GRB distances as well as their isotropic/non-isotropic nature of
emission. More
than 30 GRB fields have been probed by us during 1999 to 2003, out of
which
optical observations were obtained successfully for 14 GRB afterglows.
Important results derived from their light curves, spectral energy
distributions and
energetics are summarized. In general, early time
ux decay constant (~1.1)
becomes steeper (~2.4) at later times. Most of them are having
relatively
flat
spectral index with values ranging from 0.7 to 1.0. Observations of
these after-glows support the model of non-isotropic synchrotron emission
from the
center of the GRBs which reduces the budget of isotropic energy emission
from (>/=) 1053
ergs to <1052 ergs, a value which is compatible with the current
popular model
of the origin of GRBs. Recent optical and radio observations of
GRB030329
clearly indicates the association of Supernova with the GRB event.
Keywords: Gamma-ray bursts, GRB afterglows, flux decay, spectral index.