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GRB 021004 preprint information Dear Colleagues, The following paper by the VSNET Collaboration will be of interest, although the burst is not a contemporaneous one. (Uemura et al., PASJ Letters in press, also in astro-ph/0303119) Abstract We report optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB 021004. Our observation revealed the existence of a short plateau phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid fading phase. This plateau phase lasted for about 2 hours from 0.024 to 0.10 d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB 990123. We propose that the plateau phase can be interpreted as the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB 021004 is a common nature of GRB afterglows. For more details, see http://www.kusastro.kyoto-u.ac.jp/vsnet/GRB/grb021004.html Regards, Taichi Kato
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