TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1593 SUBJECT: GRB 021004: Optical Decay DATE: 02/10/06 21:11:14 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern, N. Mirabal, E. K. Armstrong, C. C. Espaillat (Columbia), J. Kemp (Joint Astronomy Centre and Columbia) report for the MDM GRB follow-up team: "Continued monitoring of the optical afterglow of GRB 021004 with the MDM 1.3m yields the following measurements on On 2002 Oct 6 UT: -------------------- UT R +/- -------------------- 02:41 19.84 0.03 07:03 19.91 0.02 11:39 20.00 0.02 -------------------- Here we used the revised calibration of Henden (GCN #1583) in which the reference has star has R=15.52. Previous R magnitudes reported in GCN #1578 would have to be decreased by 0.12 to match this reference. The mean R-band decay between 8 and 48 hours as determined by the NOT and MDM measurements can be described as a power law of slope -1.05, but with highly significant deviations from a power law (Winn et al., GCN #1576) that are robust against cross-calibration issues." An updated decay curve will be maintained at: http://www.astro.columbia.edu/~jules/021004.ps