TITLE: GCN CIRCULAR NUMBER: 41936 SUBJECT: GRB 250916A: CrAO ZTSh R-band optical observations DATE: 25/09/22 11:24:20 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO) report on behalf of IKI-GRB-FuN. We observed the field of the GRB 250916A (The Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al., GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, GCN 41876) with the Shajn 2.65m telescope of CrAO, equipped with CCD-photometer. The observations in the R-filter were carried out on epochs 2025-09-19, 2025-09-20, and 2025-09-21. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870; Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; Hall et al., GCN 41921; Moskvitin et. al, GCN 41934) is clearly detected in the stacked images taken on each epoch. Preliminary results of our observations are given below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-09-19 21:40:39 3.42451 120*120 R 21.45 0.02 25.0 2025-09-20 23:47:56 4.48374 78*120 R 21.89 0.03 24.7 2025-09-21 22:21:48 5.44545 109*120 R 22.72 0.05 24.8 Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted via Lupton 2005 transformations) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41936. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...