Optical observations of GRB afterglows from 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 (>/=) 10/sup53/ ergs to <10/sup52/ 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