TITLE: GCN CIRCULAR NUMBER: 38709 SUBJECT: GRB 241228A: Mondy optical afterglow observations DATE: 24/12/29 16:43:08 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com> A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (HSE) report on behalf of GRB IKI FuN: We observed the field of GRB 241228B triggered by Fermi (Fermi GBM team, GCN 38682) with AZT-33IK telescope of Mondy observatory in R-filter starting on (UT) 2024-12-28 19:42:31. We clearly detect optical afterglow (Kumar et al., GCN 38684 and GCN 38691; An et al. GCN 38687; Ortega-Casas et al., GCN 38692; Ghosh et al., GCN 38702; An et al., GCN 38704). Preliminary photometry of the afterglow is the following Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2024-12-28 19:42:31 0.66628 30x120 R 20.28 0.04 23.0 The photometry is based on nearby SDSS DR16 stars (R mags by Lupton transformation). View this GCN Circular online at https://gcn.nasa.gov/circulars/38709. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...