TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1585 SUBJECT: GRB 021004: Optical Photometry at 1.5 Days DATE: 02/10/06 02:29:36 GMT FROM: Stephen Holland at U. of Notre Dame GRB 021004: Optical Photometry at 1.5 Days S. Holland (Notre Dame), J. P. U. Fynbo, M. Weidinger (Aarhus) M. P. Egholm (NOT), and A. Levan (Leicester) on behalf of a larger collaboration report: We have obtained deep R-band images of the field containing GRB 021004 using the 2.56-meter Nordic Optical Telescope on La Palma on Oct. 6.0 UT. The optical afterglow of GRB 011211 is visible in our images. Using the comparison star from Fox et al. (2002, GCN 1564) and the calibration of Henden (2002, GNC 1583) we find the following preliminary magnitudes: Date UT t(days) Rc Err ------------------------------------- Oct. 5 20:24:58 1.346 19.54 0.04 Oct. 5 20:36:28 1.354 19.53 0.04 Oct. 5 22:22:31 1.428 19.62 0.05 Oct. 6 00:10:41 1.503 19.66 0.04 These magnitudes imply that the optical afterglow faded at a rate of alpha = -1.08 during the four hours that these observations were taken. Combining these magnitudes with those of Weidinger et al. (2002, GCN 1573) suggests that the optical afterglow has decayed with a constant slope of alpha = -1.01 between 0.09 and 1.50 days after the burst. A plot of our preliminary Rc-band light curve is available at . This message may be cite