TITLE: GCN CIRCULAR NUMBER: 6288 SUBJECT: GRB 070411: Optical photometry at Crni Vrh DATE: 07/04/12 13:15:01 GMT FROM: Herman Mikuz at OCV H. Mikuz, J. Skvarc and B. Dintinjana on behalf of PIKA observing program at Crni Vrh Observatory: Following the GCN 6270, we performed the analysis of images, obtained with R and B photometric filters. Photometry results are given in table below. Time refers to exposure start. Time (UT) h m s Exposure (s) Mag. Err. Filter 2007 Apr 11 20:14:00.8 90 18.7 0.2 R 2007 Apr 11 20:19:31.8 90 18.2 0.2 R 2007 Apr 11 20:25:02.7 90 18.4 0.2 R 2007 Apr 11 20:30:33.6 90 18.8 0.3 R 2007 Apr 11 20:36:04.3 90 19.7 0.7 R 2007 Apr 11 20:41:35.2 90 not detected R 2007 Apr 11 20:16:00.9 180 19.9 0.7 B 2007 Apr 11 20:21:32.0 180 19.1 0.3 B 2007 Apr 11 20:27:03.0 180 19.3 0.3 B 2007 Apr 11 20:32:33.9 180 19.9 0.6 B 2007 Apr 11 20:38:04.6 180 not detected B 2007 Apr 11 20:43:35.3 180 not detected B The magnitudes are derived using comparison stars from the USNO-B1 catalogue. The 3-sigma limiting magnitude in R filter is around magnitude 19.8, and about 20.0 in B filter. Fits images are available at http://www.observatorij.org/Data/GRB/2007-04-11/GRB070411.tgz