TITLE: GCN CIRCULAR NUMBER: 35826 SUBJECT: GRB 240225B: Mondy afterglow observations DATE: 24/02/28 07:44:44 GMT FROM: Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI, HSE) report on behalf of IKI-GRB-FuN: We observed the field of GRB 240225B (Nakajima et al., GCN 35796; Evans, GCN 35797, Joshi et al., GCN 35798; D'Ai et al., GCN 35810; Kawakubo et al., GCN 35811) with AZT-33IK telescope of Sayan observatory (Mondy) equipped with CMOS-photometer ANDOR NEO. We took 60x120 sec frames in the R-filter starting on 2024-02-26 (UT) 12:30:03. The optical afterglow (Gompertz et al., GCN 35805; Liu et al., GCN 35812; Malesani et al., GCN 35819; Wise et al., GCN 35820; Gompertz & Malesani, GCN 35824) is well detected in the stacked frame with a total exposure of 59x120 sec. Photometry of the optical afterglow is following: Date UT-start t-T0 Exp Filter OT Err UL FWHM (UT) (mid.) (nxT) (3sigma) (arcsec) 2024-02-27 13:01:23 1.71919 59x120 R 19.16 0.09 22.8 2.1 The magnitudes were calibrated using nearby USNO-B1.0 stars (R2 magnitudes). View this GCN Circular online at https://gcn.nasa.gov/circulars/35826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...