TITLE: GCN CIRCULAR NUMBER: 8170 SUBJECT: GRB 080903: ROTSE-III Optical Limits DATE: 08/09/03 02:12:02 GMT FROM: Fang Yuan at ROTSE F. Yuan (U Mich), W. Rujopakarn (Steward), H. Swan (U Mich), D.A. Smith (Guilford), T. Guver (U Arizona) report on behalf of the ROTSE collaboration: ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe, Turkey, responded to GRB 080903 (Swift trigger 323542; Grupe et al., GCN 8169), producing images beginning 6.7 s after the GCN notice time. An automated response took the first image at 01:12:47.7 UT, 24.4 s after the burst, and during the gamma-ray emission, under fair conditions. We took 10 5-sec, 10 20-sec and 30 60- sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Imaging is on going. Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle or the XRT error circle, for both single images and coadding into sets of 10. Individual images have limiting magnitudes ranging from 16.5-17.7; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 01:12:47.7 01:14:55.9 128 17.7 24.4 Y 01:15:04.6 01:19:42.4 277 18.3 161.3 Y