TITLE: GCN CIRCULAR NUMBER: 41981 SUBJECT: GRB 250924A: SAO RAS optical observations DATE: 25/09/25 10:53:27 GMT FROM: Alexander Moskvitin at SAO RAS <mosk@sao.ru> A. Moskvitin (SAO), V. Goranskij (SAI MSU), 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 250924A (Siegel et. al, GCN 41897; Osborne et. al, GCN 41973; Campana et. al, GCN 41974) with two SAO RAS telescopes, 1-m Zeiss-1000 equipped with the CCD-photometer on September 24/25, 23:41:32--00:27:16, and 6-m BTA equipped with the focal reducer SCORPIO-2 (Afanasiev & Moiseev, 2011, BaltA, 20, 363) on September 25, 01:42:55--01:58:24 UT. The optical transient (Siegel et. al, GCN 41959; Becerra et. al, GCN 41960; Schneider et. al, GCN 41963; Freeberg et. al, GCN 41968; Pankov et. al, GCN 41969; Zheng and Filippenko, GCN 41970; Siegel, GCN 41975; Ma et al., GCN 41976; Cotter et al., GCN 41980; and also observed in NIR, Mo et. al, GCN 41972) is clearly detected in our stacked frames. Preliminary results are as following. Date UTstart Exptime t-T0 Filter OT Err. UL Tel. s (mid, days) (3sigma) 2025.09.24 23:41:32 2520 0.65689 Rc 23.18 +/- 0.24 23.5 1-m 2025.09.25 01:42:55 600 0.73068 Rc 23.07 +/- 0.10 24.3 6-m The photometry calibrated against nearby USNO-B1.0 stars (R2 magnitudes) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41981. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...