TITLE: GCN CIRCULAR NUMBER: 5752 SUBJECT: GRB 061025: ROTSE-III Optical Limits DATE: 06/10/25 19:55:31 GMT FROM: Eli Rykoff at U of Michigan/ROTSE E.S. Rykoff (U Mich), B. E. Schaefer (Louisiana State), R. Quimby (U Texas), H. Swan (U Mich), S.A. Yost (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 061025 (Integral trigger 3525, Mereghetti, et al, GCN 5751), producing images beginning 4.6 s after the GCN notice time. An automated response took the first image at 18:36:46.6 UT, 44.7 s after the burst, under excellent conditions. We took 10 5-sec, 10 20-sec and 31 60-sec eposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Comparison to the DSS (second epoch) reveals no new sources within the 90% INTEGRAL error circle, for both single images and coadding into sets of 10; however, we are limited as the field is somewhat crowded. We note that the bright elliptical galaxy NGC 6851 is in the error box. Individual images have limiting magnitudes ranging from 13.3-16.9; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 18:36:46.6 18:36:51.6 5 15.2 44.7 N 18:36:46.6 18:39:01.9 135 16.9 44.7 Y 18:39:11.4 18:43:57.0 285 17.5 189.5 Y