TITLE: GCN CIRCULAR NUMBER: 1597 SUBJECT: GRB 021004: Optical Photometry at 2.5 Days DATE: 02/10/07 19:16:17 GMT FROM: Stephen Holland at U. of Notre Dame GRB 021004: Optical Photometry at 2.5 Days S. T. Holland (Notre Dame), J. P. U. Fynbo, M. Weidinger (Aarhus) M. P. Egholm (NOT), A. Levan (Leicester), J. Hjorth and H. Pedersen (Copenhagen) on behalf of a larger collaboration report: We have obtained deep Rc-band images of the field containing GRB 021004 using the 2.56-meter Nordic Optical Telescope on La Palma on the evening of Oct. 6 UT. The optical afterglow of GRB 021004 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. 6 19:57:07 2.327 20.12 0.10 Oct. 6 20:37:26 2.355 20.08 0.01 Oct. 6 21:56:38 2.410 20.16 0.03 Oct. 6 22:08:09 2.418 20.15 0.03 These magnitudes, and those of Holland et al. (2002, GCN 2002), imply that the optical afterglow faded at a rate a rate of alpha = -0.9 between 32 and 58 hours after the burst. We note that that the optical afterglow appears to be fading less slowly than it did between 12 and 17 hours after the burst. A deep Rc image constructed from all of our data shows no evidence for a host galaxy. A plot of our preliminary Rc-band light curve is available at . This message may be cited.