TITLE: GCN CIRCULAR NUMBER: 38539 SUBJECT: GRB 241209B: Mondy AZT-33IK and AbAO AS-32 optical observations DATE: 24/12/12 06:24:33 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN: We performed optical observations of GRB 241209B (Xie et. al, GCN 38478; Evans, GCN 38494; Perez-Garcia et. al, GCN 38499; Qiu et. al, GCN 38516; Williams et. al, GCN 38525; DeLaunay et. al, GCN 38528; Dafcikova et. al, GCN 38534; Ridnaia et. al, GCN 38537) in the R-filter with 1.5-meter AZT-33IK telescope of Sayan observatory (Mondy) and 0.7-meter AS-32 telescope of Abastumani observatory (AbAO). The observations began at Mondy on 2024-12-10 18:11:43 UT, i.e. ~1.6 days since trigger. The optical counterpart (Xie et. al, GCN 38478) is not detected in the stacked images from both telescopes. The preliminary upper limits are given below: Date UTstart t-T0 Exp. Filter OT Err. UL Telescope (mid, days) (s) (3sigma) 2024-12-10 18:11:43 1.621802 40*120 R n/d n/d 22.1 AZT-33IK 2024-12-10 21:27:04 1.759885 87*60 R n/d n/d 20.9 AS-32 2024-12-11 20:35:13 2.722143 41*120 R n/d n/d 21.8 AZT-33IK The magnitudes were calibrated using nearby stars from USNO-B1.0 (R2 magnitudes) and are not corrected for the Galactic extinction towards the GRB 241209B. View this GCN Circular online at https://gcn.nasa.gov/circulars/38539. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...