TITLE: GCN CIRCULAR NUMBER: 44663 SUBJECT: GRB 260509A: CrAO ZTSh optical upper limit DATE: 26/05/18 13:50:25 GMT FROM: Alexander Moskvitin at SAO RAS <mosk@sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO), N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN. We observed the field of the GRB 260509A (Götz et al., GCN 44504) with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO). We obtained 40*120 s exposures R filter on 2026-05-15 19:45:59--21:09:48 UT (5.94218 days after trigger). We did not detect the OT (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Sánchez Álvarez et al., GCN 44509; Zheng et al., GCN 44510; Kechin et al., GCN 44512; Belkin, GCN 44513; Corcoran et al., GCN 44514; Bochenek and Perley, GCN 44516; Moskvitin and Spiridonova, GCN 44563; Mo et al., GCN 44590; Li et al., GCN 44598) down to the 3-sigma limiting magnitude of R_lim = 24.2. This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44663. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...