TITLE: GCN CIRCULAR NUMBER: 42256 SUBJECT: GRB 251013C NUTTelA-TAO / BSTI Early Measurements DATE: 25/10/14 13:45:06 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), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 251013C on receipt of an automated GCN SVOM/ECLAIRs position alert, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We started observations at UT 2025 October 13, 17:41:17, 95 s after the ECLAIRs trigger (N. A. Rakotondrainibe, et. al., GCN 42222). Observations were made in conditions that started good and deteriorated to cloudy over the night. A new and changing source consistent with the XRT position (P.A. Evans et al., GCN 42232) was detected. Note that these observations provide essentially full-time coverage until conditions deteriorated, about 3 hours of coverage. The source was off our field in g' and r' band cameras, but on the sensor with adequate margin in our Sloan i' camera. We report the following preliminary, uncorrected, selected photometric values for the optical transient: tc-t0(s) texp i'(mag) err(mag) -------- ------ ------- -------- 96 3.0 13.67 0.1 123 3.0 14.20 0.1 141 3.0 14.27 0.1 185 30.0 14.69 0.06 245 30.0 14.96 0.06 305 30.0 15.16 0.06 425 30.0 15.06 0.06 635 30.0 15.14 0.06 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 find a rapid fading to a plateau starting at ~300 s. 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/42256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...