TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5213 SUBJECT: GRB 060604A: ROTSE-III Optical Limits DATE: 06/06/04 19:06:43 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State) reports on behalf of the ROTSE collaboration: ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB 060604A (Swift trigger 213486), producing images beginning 5.0 s after the GCN notice time. An automated response took the first image at 18:19:59.1 UT, 59.0 s after the burst, under excellent conditions. We took 10 5-sec, 10 20-sec and 20 60-sec eposures, with more ongoing. These unfiltered images are 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; the field is not crowded. The XRT position and the UVOT position (M. J. Page et al. 2006, GCN 5212) has two faint stars nearby which might mask the fast fading optical transient. Individual images have limiting magnitudes ranging from 15.2-16.9; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 18:19:59.1 18:20:19.1 20 15.8 59.0 N 18:29:37.6 18:41:55.8 738 17.9 637.5 Y