TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3867 SUBJECT: GRB 050824: ROTSE-III Optical Limits DATE: 05/08/25 01:58:31 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State), Fang Yuan (U Mich), and K. Alatalo (Berkeley) report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 050824 (Swift trigger 151905), producing images beginning 7.1 s after the GCN notice time. An automated response took the first image at 23:22:02.1 UT, 585.8 s after the burst, under good conditions although with the gibbous Moon only 25 degrees away. We took 10 5-sec, 10 20-sec and 130 60-sec eposures. These unfiltered images are calibrated relative to USNO A2.0 (R). ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe, Turkey, also responded, producing images beginning 5.8 s after the GCN notice time. An automated response took the first image at 23:22:00.8 UT, 584.5 s after the burst, under good conditions (but again, with the gibbous Moon nearby). We took 10 5-sec, 10 20-sec and 80 60-sec eposures. These unfiltered images are also calibrated relative to USNO A2.0 (R). Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma error circle, for both single images and coadding into sets of 10. Individual images have limiting magnitudes ranging from 15.4-17.0; we set the following specific limits. ROTSE start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------------- III-c 23:22:02.1 23:23:27.1 85 17.3 585.8 Y III-c 23:23:27.7 23:28:21.7 294 18.2 671.4 Y III-d 23:22:00.8 23:24:20.8 140 17.4 584.5 Y III-d 23:24:21.5 23:29:20.5 299 17.9 725.2 Y In particular, we do not see the new source described by Gorosabel et al. (GCN 3865), with this source being near or below our detection threshold.