TITLE: GCN CIRCULAR NUMBER: 33608 SUBJECT: GRB 230409B: Mondy optical upper limit DATE: 23/04/12 23:21:33 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), E. Klunko (ISTP), A. Pozanenko (IKI), N. Pankov (HSE) report on behalf of GRB IKI FuN: We observed the field of Swift GRB 230409B (Beardmore et al., GCN 33592) with AZT-33IK telescope of Mondy observatory in R-filter on 2023-04-09 starting (UT) 14:52:05. We do not detect the optical counterpart (Kuin et al., GCN 33595) within the enhanced Swift/XRT error box (Evans et al., GCN 33594). Preliminary photometry of a stacked image is following Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2023-04-09 14:52:05 0.42231 26*60 R n/d n/d 20.5 The photometry is based on nearby USNO-B1.0 stars. USNO-B1.0 RA DEC R2 21:58:01.9195200 +52:49:21.982800 15.15 21:58:13.7054400 +52:48:57.002400 15.56 21:57:54.5028000 +52:50:57.080400 15.95 The upper limit does not contradict result reported by Adami et al. (GCN 33607).