TITLE: GCN CIRCULAR NUMBER: 39094 SUBJECT: GRB 250128B: SAO RAS Zeiss-1000 and CrAO ZTSh optical upper limits DATE: 25/01/30 07:15:01 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com> A. S. Moskvitin (SAO RAS), N. Pankov (HSE, IKI), O. Spiridonova (SAO RAS), V. Rumyantsev (CrAO), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of the collaboration between IKI-GRB-FuN and the GRB follow-up team. We observed the field of GRB 250128B (Fermi GBM team, GCN 39057; Evans et al., GCN 39058; Myers and Meegan, GCN 39063; Osborne et al., GCN 39064) with the 1-meter Zeiss-1000 telescope at the Special Astrophysical Observatory (SAO RAS) and the 2.6-meter Shajn telescope (ZTSh) at Crimean Astrophysical Observatory (CrAO). The observations began on 2025-01-29 00:57:27 at the SAO RAS, i.e. ~0.38 days since the burst. We obtained 12 x 300 sec images in the Rc-filter with Zeiss-1000 and 44 x 120 sec images in the R-filter with ZTSh. The stacked images from both telescopes have not revealed any new optical source located within the enhanced XRT circle (Evans et al., GCN 39069). The preliminary upper limits are as follows: Date UT start t-T0 Exp. Filter UL(3sigma) Telescope (mid, days) (s) 2025-01-29 00:57:27 0.38090 12*300 Rc 23.5 Zeiss-1000 2025-01-29 01:33:22 0.41284 44*120 R 23.1 ZTSh The photometry is based on nearby stars of the USNO-B1.0 catalog (R2 magnitudes) and have not been corrected for the Galactic extinction. Our results are consistent with the upper limits obtained by other teams (Izzo & Malesani, GCN 39059; Lipunov et al., GCN 39061; GCN 39067; Ulaczyk et al., GCN 39062; Adami et al., GCN 39076; Becerra et al., GCN 39080; Heintz et al., GCN 39081; Yang et. al, GCN 39084; Rossi et. al, GCN 39086). View this GCN Circular online at https://gcn.nasa.gov/circulars/39094. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...