GCN Circular 3238
R. M. Quimby (UTexas), E. S. Rykoff (UMich) and B. E. Schaefer (LSU) report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas responded automatically to Swift GRB050412 (Trigger #114485), producing images beginning 7.1 seconds after receiving the GCN trigger under excellent conditions. The first image was taken at 05:44:48.0 UT, 45.1 seconds after the burst. We have taken ten 5 second, ten 20 second and forty 60 s exposures and imaging is ongoing. The images are unfiltered and were calibrated relative to USNO A2.0. Individual images have limiting magnitudes ranging from 17.5-19.1. Comparison to DSS (second epoch) reveals no new sources within the 3-sigma BAT error circle to a limiting magnitude of 17.5 for the first 5 second exposure. Coadding the images into sets of 10 revels no new sources down to 19.1, 19.9 (beginning 05:45:52.1), and 20.3 (beginning 05:50:43.4) magnitude. Analysis is ongoing.