TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4999 SUBJECT: GRB 060421: TTT Observations DATE: 06/04/24 02:50:10 GMT FROM: Chelsea Louise MacLeod at UNC-Chapel Hill/PROMPT C. MacLeod, J. Harvey, A. Trotter, M. Nysewander, A. LaCluyze, D. Reichart, A. Crain, K. Ivarsen, A. Foster, J. Haislip, J. Kirschbrown, and J. Carpenter report on behalf of the UNC team of the FUN GRB Collaboration: Skynet observed the localization of GRB 060421 (Goad et al., GCN 4985; Goad & Page, GCN 4987; Goad, Page & Burrows, GCN 4992) with 14.5-inch TTT in Colorado beginning 2.2 hours after the burst in variable conditions: Filter Start (UT) Stop (UT) Exposures Total (min) Red* 02:49:45 03:12:03 6 x 160s 16.0 Green** 03:13:48 03:34:41 6 x 160s 16.0 Blue 03:35:51 03:54:51 5 x 160s 13.3 Red* 03:57:17 04:15:58 5 x 160s 13.3 Green** 04:19:00 05:00:41 11 x 160s 29.3 Blue 05:02:14 05:42:19 11 x 160s 29.3 Red* 05:44:56 06:28:07 11 x 160s 30.7 + 1 x 80s Green** 06:29:39 07:12:54 11 x 160s 29.3 Blue 07:14:37 07:55:35 11 x 160s 29.3 Red* 07:57:16 09:20:36 19 x 160s 50.7 Green** 09:22:42 10:45:43 21 x 160s 56.0 Blue 10:48:00 11:06:50 5 x 160s 13.3 * Approximates R band ** Approximates V band No new source is found to V > 18.3 mag (3 sigma; calibrated to five NOMAD stars) at 4.0 hours after the burst.