TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1589 SUBJECT: GRB 021004: Optical observations at RIKEN DATE: 02/10/06 09:09:05 GMT FROM: Ken ichi Torii at RIKEN K. Torii (RIKEN), T. Kato (Kyoto Univ.), and H. Yamaoka (Kyushu Univ.) report: In response to the GCN/HETE burst position notice, a part of the error region of GRB 021004 (Shirasaki, et al., GCN 1565) was observed by the automated system at RIKEN. Starting at 12:09:27 UT (193-s after the burst trigger), 30-s exposures were repeated with the 0.20-m reflector equipped with unfiltered CCD AP7p. Frequent passages of clouds significantly degraded the limiting magnitudes of the data. The optical afterglow reported by Fox (GCN 1564) is not visible in our early phase images. Comparison with the USNO-A2.0 red magnitudes gave the following 3-sigma upper limits for the afterglow. Further analyses for the full data set are in progress. ---------------------------------------- Mean epoch From GRB Magnitude ---------------------------------------- 12:09:42 UT 208 s > 13.6 12:10:21 247 > 13.6 12:11:00 286 > 13.6 12:11:40 326 > 14.2 12:12:19 365 > 13.6 ----------------------------------------