TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4294 SUBJECT: GRB 051021 Optical Observations DATE: 05/11/20 05:37:23 GMT FROM: T.P. Prabhu at Indian Astro. Obs. D.K. Sahu, G. Pandey, P. Bama and N.K. Chakradhari (Indian Institute of Astrophysics, Bangalore,India) communicate on behalf of a larger Indian collaboration: We observed the error box of the HETE trigger 3947 in Bessell R and I filters with the 2-m Himalayan Chandra Telescope, Hanle, India, between 20:25 UT and 21:00 UT, 2005 October 21 (about 7 hours after the burst). We could clearly detect the OT of GRB 051021 reported by Fox et al. (GCN 4120) with effective exposures of 600s (2x300s) in R and 900s (3x300s) in I band. The preliminary magnitudes for the OT, estimated using the calibration provided by Henden (GCN 4184) are as follows: Filter Mean Mid-UT Magnitude R 20:43 21.51+/-0.15 I 20.43 20.93+/-0.10 This message may be cited.