TITLE: GCN CIRCULAR NUMBER: 42868 SUBJECT: GRB 251126A NUTTelA-TAO Early Measurements DATE: 25/11/28 10:49:00 GMT FROM: Zhanat Maksut at Nazarbayev University <zhanat.maksut@nu.edu.kz> Z. Maksut (NU), B. Grossan (UCB, NU), T. Komesh (NU), E. Abdikamalov (NU), M. Krugov (FAI) and D. Berdikhan (NU) The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 251126A on receipt of an automated GCN / BAT position alert, observing in Sloan g' and i' bands with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). Observations started at UT 2025 November 26, 19:11:32, 52 s after the SWIFT/BAT trigger (Caputo et al., GCN 42843). Weather conditions were good within the first 1 hour of observation, but gradually deteriorated to cloudy over the course of the night. A new optical counterpart reported by Swain et al., GCN 42844; Fu et al., GCN 42848; Reguitti et al., GCN 42849; Broens et al., GCN 42850; Angulo et al., GCN 42855; Pulido-Torres et al., GCN 42856; Gupta et al., GCN 42857; Cotter et al., GCN 42858; Seki et al., GCN 42859, was detected. We report the following preliminary, uncorrected, selected photometric values for the optical transient: tc-t0(s) t_exp i'(mag) err(mag) g’(mag) err(mag) -------- ------ ------- -------- 76 48.0 18.12 0.08 19.49 0.06 142 30.0 17.38 0.07 18.96 0.06 322 30.0 17.62 0.08 19.03 0.09 502 30.0 17.88 0.09 19.31 0.08 tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars on our images (see Komesh, T. et al. 2023, MNRAS 520, 6104). We caution the reader that these are preliminary results, without color or other corrections, and will likely change. Please also note that times are approximate. Systematic errors are estimated from previous measurements. We welcome requests for additional data. ---------------------------------- NU = Nazarbayev University, Astana, Kazakhstan UCB = University of California, Berkeley, USA FAI = Fesenkov Astrophysical Institute, Kazakhstan 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, Kazkhstan. View this GCN Circular online at https://gcn.nasa.gov/circulars/42868. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...