TITLE: GCN CIRCULAR NUMBER: 41948 SUBJECT: GRB 250920B: SAO RAS optical observations DATE: 25/09/22 22:46:39 GMT FROM: Alexander Moskvitin at SAO RAS <mosk@sao.ru> A. Moskvitin, O. Spiridonova (SAO), N. Pankov (HSE), A. Pozanenko (IKI) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250920B (Fermi GBM Team, GCN 41897; Gupta et al., GCN 41898; Page et al., GCN 41909; Evans et al., GCN 41910; Sonawane and Meegan, GCN 41919; Sakamoto et al., GCN 41923; Cheung et al., GCN 41937; Svinkin et al., GCN 41942) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained 10 x 300 sec. images Rc band on September 22, 16:22:43--17:17:34 (t_mid - T0 = 2.33586 days). The optical transient (Gupta et al., GCN 41898; Wu et al., GCN 41908; Hall et al., GCN 41914; Kuin and Gupta, GCN 41915; Reguitti et al., GCN 41932) is clearly detected in the stacked frame with the brightness of R = 21.7 +/- 0.1. Date UT start t-T0 Exp. Filter OT Err. UL (3sigma) (mid, d) (s) 2025.09.22 16:22:43 2.33586 10 x 300 Rc 21.7 +/- 0.1 23.2 Preliminary photometry is based on the nearby stars from USNO-B1 (R2 magnitudes) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41948. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...