TITLE: GCN CIRCULAR NUMBER: 11179 SUBJECT: GRB 100901A: ROTSE-III Detection DATE: 10/09/02 19:20:08 GMT FROM: Shashi Bhushan Pandey at ROTSE S. B. Pandey and W. Zheng (U Mich), report on behalf of the ROTSE collaboration: Due to bad weather conditions, the ROTSE-3a telescope at Siding Springs Observatory, Australia did not respond to GRB 100901A (Swift trigger 433065, Immler S. et al., GCN 11159). Automated re-pointing of ROTSE-3c at the H.E.S.S. site at Mt. Gamsberg, Namibia and ROTSE-3b at the McDonald Observatory, Texas observed the optical afterglow starting ~ 8.6 to 22.0 hours after the burst. The optical afterglow was detected in all the stacked frames. The optical afterglow candidate appears to decay with a power-law index of ~1.2 at later epochs. Further imaging is ongoing.