TITLE: GCN CIRCULAR NUMBER: 43237 SUBJECT: GRB 251222A: NUTTelA-TAO Early Measurements DATE: 25/12/25 13:23:54 GMT FROM: Zhanat Maksut at Nazarbayev University <zhanat.maksut@nu.edu.kz> Z. Maksut (NU), B. Grossan (UCB, NU), T. Komesh (NU), D. Berdikhan (NU), E. Abdikamalov (NU), M. Krugov (FAI), K. Baigarin (NU), M. Coughlin (UNM), P. Hello (IJCLAB), S. Antier (IJCLAB), and S. Karpov (FZU) on behalf of the GRANDMA/NUTTelA-TAO: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 251222A on receipt of an automated SVOM/ECLAIRs position alert. Observations started at 17:07:10 UT on 2025-12-22, 84 s after the SVOM/ECLAIRs trigger (Yang et al., GCN 43188). We observe in Sloan g' and i' bands simultaneously with the Burst Simultaneous Three-Channel Imager (Grossan, Kumar & Smoot 2019, JHEA, 32, 14). A new optical counterpart reported previously (Palmerio et al., GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229) was detected. We observe a rapid decay during the first ∼100 s, followed by a gradual rise leading to the first bump at around 500 s. The light curve then exhibits a decay until ∼4000 s, after which it rises again, reaching a second bump at around 10 ks. The total duration of the observations was about 4.5 hours. We report the following preliminary, uncorrected, selected photometric values: tc-t0(s) t_exp i'(mag) err(mag) g’(mag) err(mag) -------- ------ ------- -------- 85.5 3.0 16.2 0.08 17.02 0.09 117 30.0 17.58 0.07 19.45 0.09 519 30.0 17.32 0.08 18.22 0.07 3161 180.0 19.3 0.09 19.95 0.08 tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars (see Komesh, T. et al. 2023, MNRAS 520, 6104). We caution that these are preliminary results, without color or other corrections. This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazakhstan. 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/43237. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...