TITLE: GCN CIRCULAR NUMBER: 30582 SUBJECT: GRB 210731A: KAIT Optical Detection DATE: 21/08/02 09:19:57 GMT FROM: Weikang Zheng at UC Berkeley WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to the Swift GRB 210731A (Troja et al., GCN 30568) starting at ~9.04 hours after the Swift trigger. A total of 30x60s images were obtained in the clear (roughly R) filter. The optical afterglow (de Wet et al., GCN 30571; Kuin et al., GCN 30572; Guelbenzu et al., GCN 30574; Lipunov et al., GCN 30578;) was clearly detected in each single image. We measured its brightness of 18.6 +/- 0.1 mag at 9.26 hours after burst, calibrated to the Pan-STARRS1 catalog.