Very Early Multicolor Observations of the Plateau Phase of the GRB 041006 Afterglow

We present observations of the optical afterglow of GRB 041006 with the Kiso Observatory 1.05 m Schmidt telescope, the Lulin Observatory 1.0 m telescope, and the Xinglong Observatory 0.6 m telescope. Three bands (B, V, and R) of photometric data points were obtained on 2004 October 6, 0.025-0.329 days after the burst. These very early multiband light curves imply the existence of a color-dependent plateau phase. The B-band light curve shows a clear plateau at around 0.03 days after the burst. The R-band light curve shows the hint of a plateau, or a possible slope change, at around 0.1 days after the burst. The overall behavior of these multiband light curves may be interpreted in terms of the sum of two separate components, one showing a monotonic decay, the other exhibiting a rising and a falling phase, as described by the standard afterglow model.