GCN Circular 3190
GRB 050408: ROTSE-III Optical Limits D.A. Smith, S.A. Yost, & E.S. Rykoff (U of Michigan) report on behalf of the ROTSE collaboration: ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB 050408 (HETE trigger 3711). An automated response produced images beginning at 16:23:09.4 UT, 18.5 s after the trigger time and 6.6 s after the alert was distributed. The first few images were therefore recorded while the burst was still active at high energies (Sakamoto et al., GCN Circ. #3189). The telescope took 10 5-sec, 10 20-sec, and a series of 60-sec eposures. These unfiltered images are calibrated relative to USNO A2.0 (R). The ROTSE-III images show strong and increasing degredation from clouds. After the 20th image (~7.7 min after the trigger time), clouds became opaque enough to render many images useless. Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma SXC error circle. Individual images have limiting magnitudes ranging from 14.7-16.9. In particular, we set a limit of magnitude 14.7 in the first 5 s exposure. Coadding the first ten images yields a limiting magnitude of 15.1, and coadding the 20-s images (165.5-522.5 s after the trigger time) yields a limiting magnitude of 17.8.