TITLE: GCN CIRCULAR NUMBER: 6076 SUBJECT: GRB 070208: ROTSE-III Optical Limits DATE: 07/02/08 10:13:07 GMT FROM: Fang Yuan at ROTSE F. Yuan (U Mich), W. Rujopakarn (U Arizona), H. Swan (U Mich), E. S. Rykoff (U Mich) report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 070208 (Swift trigger 259714, GCN 6074, Sato, et al), producing images beginning 5.8 s after the GCN notice time. An automated response took the first image at 09:11:14.8 UT, 40.5 s after the burst, under fair conditions. We took 10 5-sec, 10 20-sec and 20 60-sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Comparison to the DSS (second epoch) reveals no new sources within both the BAT and the XRT error circles, for both single images and coadding into sets of 10. We marginally detect one of the DSS objects detected by Mirabal & Halpern (GCN 6075) in our deepest images. Individual images have limiting magnitudes ranging from 15.9-17.0; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 09:11:14.8 09:11:19.8 5 16.0 40.5 N 09:11:14.8 09:12:21.9 67 17.5 40.5 Y 09:12:29.9 09:17:25.5 295 18.2 115.6 Y