TITLE: GCN CIRCULAR NUMBER: 23033 SUBJECT: GRB 180720B: KAIT Optical Observations DATE: 18/07/25 00:12:38 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, observed the field of Swift GRB 180720B (Siegel et al., GCN 22973) each night from 21 to 24 UT, at a mean time of 0.855, 1.886, 2.883 and 3.874 days, respectively, after the burst. Observations were performed with a sequence in the B, V, R, I and clear (roughly R) filters, and the exposure time was 60 s per image. The optical afterglow (Martone et al., GCN 22976) was clearly detected and we measure its clear band mag to be 18.5, 19.6, 20.5 and 20.9, respectively, calibrated to the SDSS catalog.