TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1587 SUBJECT: GRB 021004: Optical Observations DATE: 02/10/06 07:10:41 GMT FROM: T.P. Prabhu at Indian Astro. Obs. D.K. Sahu, B.C. Bhatt, G.C. Anupama, T.P. Prabhu (Indian Institute of Astrophysics, Bangalore) report on behalf of a larger collaboration: GRB 021004 was observed with the HFOSC instrument on the 2-m Himalayan Chandra Telescope on 4 and 5 October 2002. The magnitudes with respect to the comparison star of Fox (GCN 1564) as calibrated by Henden (GCN 1583) on October 4 are listed below: October 4 R error UT(center) (300 s) 16:34:36 17.13 0.01 16:44:03 17.20 0.01 16:52:29 17.24 0.01 17:01:16 17.21 0.01 17:09:26 17.28 0.01 17:18:12 17.39 0.01 18:04:37 17.69 0.01 19:48:36 17.90 0.02 20:33:36 18.06 0.02 22:05:58 18.20 0.03 23:36:22 18.46 0.05 B (600s) 17:34:18 18.42 0.01 20:01:07 18.90 0.02 22:18:14 19.18 0.03 23:03:11 19.31 0.03 V (400s) 17:42:32 18.01 0.01 20:14:38 18.50 0.02 22:40:30 18.77 0.03 23:14:33 18.78 0.03 These results supersede the ones reported in GCN 1581. Preliminary magnitudes for October 5 are UT R 17:38 19.38 22:10 19.70 The decay appears to have steepened following the bump noticed by Winn et al (GCN 1576). The spectra recorded with the same instrument on October 4 show the redshift systems with z=1.38 and 1.60 (GCN 1582). The identification of z=1.72 in GCN 1582 was erroneous and is regretted. On the other hand, we confirm the presence of unidentified lines reported by Eracleous et al (GCN 1579). The message may be cited.