TITLE: GCN CIRCULAR NUMBER: 38777 SUBJECT: GRB 250101A NUTTelA-TAO / BSTI Early Measurements DATE: 25/01/02 12:04:47 GMT FROM: Toktarkhan Komesh at Nazarbayev University toktarkhan.komesh@nu.edu.kz

T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), B. Grossan (UCB, 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 250101A on receipt of an automated GCN / BAT position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14).

We started observations at 13:24:00 UT on 2025-01-01, 70 s after the BAT trigger. Observations were made in partly cloudy conditions. A new and changing source consistent with the XRT position (M.R. Goad et al., GCN 38761) was detected. Note that these observations provide essentially full-time coverage, simultaneous in two bands. We report the following photometric values for the optical transient:

tc-t0(s) g'(mag) err r'(mag) err exposure_time (s) -------------------------------------------------------------- 100.1 18.7 0.1 18.2 0.1 57 166.0 17.6 0.1 17.2 0.1 15 181.0 17.5 0.1 17.0 0.1 15 196.0 17.1 0.1 16.9 0.1 15 211.0 17.3 0.1 16.9 0.1 15 226.0 17.4 0.1 16.8 0.1 15 241.0 17.3 0.1 16.7 0.1 15 256.0 17.3 0.1 16.8 0.1 15 271.0 17.4 0.1 16.9 0.1 15 286.0 17.4 0.1 16.9 0.1 15 301.0 17.5 0.2 17.0 0.1 15 316.0 17.7 0.2 17.0 0.1 15 331.0 17.5 0.1 17.0 0.1 15 346.0 17.7 0.1 17.1 0.1 15 361.0 17.6 0.1 17.1 0.1 15 376.0 17.6 0.1 17.0 0.1 15 391.0 18.0 0.1 16.9 0.1 15 406.0 17.6 0.2 17.4 0.1 15 421.0 17.8 0.1 17.2 0.1 15 436.0 17.5 0.1 17.4 0.1 15 451.0 18.1 0.2 17.4 0.1 15 466.0 17.8 0.2 17.3 0.1 15 481.0 17.8 0.1 17.3 0.1 15 496.0 17.7 0.2 17.4 0.1 15 511.0 17.9 0.1 17.4 0.1 15 526.0 17.7 0.1 17.5 0.1 15 541.0 18.3 0.2 17.5 0.1 15 556.0 17.9 0.2 17.3 0.1 15 571.0 18.0 0.1 17.3 0.1 15 586.0 17.7 0.2 17.4 0.1 15 601.0 18.2 0.2 17.8 0.1 15 616.0 17.9 0.1 17.7 0.2 15 631.0 17.9 0.1 17.2 0.1 15 653.5 18.1 0.1 17.6 0.1 30 683.5 18.1 0.1 17.5 0.1 30 713.5 18.1 0.1 17.5 0.1 30 743.5 18.0 0.1 17.5 0.1 30 864.3 18.2 0.0 17.5 0.0 60 924.3 18.2 0.1 17.7 0.1 60 984.3 18.2 0.1 17.7 0.0 60 1044.3 18.3 0.1 17.8 0.0 60 1104.3 18.4 0.1 17.8 0.1 60 1164.3 18.3 0.1 17.8 0.0 60 1224.3 18.5 0.1 17.8 0.0 60 1284.3 18.5 0.1 17.9 0.1 60 1344.3 18.6 0.1 17.8 0.1 60 1404.3 18.4 0.1 18.0 0.1 60 1464.3 18.4 0.1 18.1 0.1 60 1524.3 18.6 0.1 18.1 0.1 60 1584.3 18.7 0.1 18.2 0.1 60 1644.3 18.7 0.1 18.3 0.1 60 1704.3 18.7 0.1 18.2 0.1 60 1764.3 18.7 0.1 18.2 0.1 60 1824.3 18.8 0.1 18.4 0.1 60 1884.3 18.8 0.1 18.4 0.1 60 1944.3 19.0 0.1 18.3 0.1 60 2004.3 18.8 0.1 18.4 0.1 60 2064.3 18.9 0.1 18.3 0.1 60 2124.3 18.8 0.1 18.3 0.1 60 2184.3 19.0 0.1 18.5 0.1 60 2244.3 19.0 0.1 18.5 0.1 60 2304.3 18.9 0.1 18.5 0.1 60 2364.3 19.2 0.1 18.4 0.1 60 2424.3 19.0 0.1 18.4 0.1 60 2484.3 19.0 0.1 18.6 0.1 60 2544.3 19.1 0.1 18.6 0.1 60 2604.3 19.0 0.1 18.8 0.1 60 2664.3 19.1 0.1 18.8 0.1 60 2724.3 18.9 0.1 18.8 0.1 60 2784.3 19.2 0.1 18.9 0.1 60 2844.3 19.2 0.1 18.8 0.1 60 2904.3 19.4 0.1 18.6 0.1 60 2964.3 19.2 0.1 18.9 0.1 60 3024.3 19.2 0.1 18.7 0.1 60 3084.3 19.2 0.1 18.7 0.1 60 3144.4 19.3 0.2 18.9 0.1 60 3204.4 19.2 0.1 19.1 0.2 60 3294.4 19.4 0.1 18.9 0.1 120 3414.4 19.4 0.1 18.7 0.1 120 3534.4 19.4 0.1 19.0 0.1 120 3654.4 19.4 0.2 19.0 0.1 120 3774.4 19.4 0.2 19.0 0.2 120 4166.8 19.7 0.1 18.9 0.1 360 4526.8 19.8 0.2 19.2 0.1 360

tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars on our images. A light curve of the optical transient is presented in Figure 1: https://ecl.nu.edu.kz/research/observations/gamma-ray-bursts/grb250101a

Our results are in agreement with those reported in previously published circulars (Li et al., GCN 38753; Mohan et al., GCN 38754; Wu et al., GCN 38758; Escudero-Coca et al., GCN 38769; Zhang et al., 38744).

We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate.

---------------------------------- 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.

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