TITLE: GCN CIRCULAR NUMBER: 10075 SUBJECT: GRB 091024: KAIT optical afterglow observations DATE: 09/10/25 02:54:09 GMT FROM: Ryan Chornock at UC Berkeley R. Chornock, W. Li, and A. V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: The Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory automatically responded to the Swift BAT trigger for GRB 091024 (Marshall et al., GCN 10062) with a sequence of observations starting 82 s after the BAT trigger. The afterglow is not initially detected. Our first detection of the optical afterglow (Mundell et al., GCN 10063) is in a 20 s I band observation starting at 08:58:45 UT. The KAIT position is (J2000) 22:36:59.64 +56:53:24.0 which is consistent the positions reported by Mundell et al. (GCN 10063) and Henden et al. (GCN 10073). The optical afterglow is thereafter detected in a sequence of V, I, and unfiltered images as it rose to a peak at an unfiltered magnitude of 16.2 (preliminarily calibrated to USNO-B1) at t=404s and then declined to mag 17.0 at t=988s, similar to the behavior described by Cano et al. (GCN 10066). After this time observations ceased due to a pointing limit.