TITLE: GCN CIRCULAR NUMBER: 43281 SUBJECT: GRB 251230A: GRANDMA/TAROT Early Detection DATE: 25/12/31 14:25:21 GMT FROM: Dalya Akl at New York University Abu Dhabi <dka2010@nyu.edu> S. Antier (IJCLAB), A. Klotz (IRAP), D. Akl (NYUAD), C. Limonta (OCA), A. Dupin (OCA), Q. André (OCA), M. Coughlin (UNM), R. Strausbaugh (EIU), Z. Maksut (NU), E. Abdikamalov (NU), P. Hello (IJCLAB), S. Karpov (FZU), M. Pillas (IAP), C. Douzet (IJCLAB), Z. Wang (BNU), N. Kochiashvili (AbAO), A. Iskandar (XAO) on behalf of GRANDMA: We observed the field of the fast X-ray transient GRB 251230A/EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263; Wang et al., GCN 43272; Sbarrato et al., GCN 43275) using TAROT/TCA with no filter. The observations started at 01:22:07 UTC on the 30th of December 2025, 36s post Swift trigger time, and lasted for 3 hours. We detected the optical afterglow candidate in the first (earliest) measurement with TAROT/TCA (60s exposure time), and we measured on 2025-12-30 01:23:19, r = 13.1 +/- 0.05 mag, after color correction. The data were reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022), using the PS1 catalogue for reference. Part of the light curve is public here on Skyportal/ICARE (https://skyportal-icare.ijclab.in2p3.fr) and also accessible in the public-report group of Skyportal: https://skyportal-icare.ijclab.in2p3.fr/public/sources/GRB-251230_012141/ver... We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). The results are consistent with other measurements reported. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/43281. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...