Early time optical observations of GRB afterglows

Abstract

Early time optical observations of GRBs are very important for revealing the prompt emission and afterglow properties of these energetic explosions. The observations of the well-studied GRBs by Swift indicate that early time properties of the optical light-curves share diverse set of features broadly consistent with the predictions made by various afterglow models though outliers exists. The comparison of a subset of wellmonitored GRBs and their early time properties at optical are compared with that seen at X-ray (Swift-XRT) and γ-ray frequencies. In most of the cases, the very early optical observations of GRBs do not trace the canonical decay nature seen at XRT frequencies, suggesting different origins for the observed early emissions in the two bands. In some of the early optical light-curves, the smooth rise and decay features are consistent with the onset of the afterglow although such features are also expected if the emission is seen off-axis and/or the outflow is structured.