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.