TITLE: GCN CIRCULAR NUMBER: 39569 SUBJECT: EP250302a: NUTTelA-TAO Early Measurments DATE: 25/03/03 12:18:23 GMT FROM: Toktarkhan Komesh at Nazarbayev University toktarkhan.komesh@nu.edu.kz

T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), D. Berdikhan (NU), B. Grossan (UCB, 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 EP250302a on receipt of an automated GCN / EP 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 15:42:43 UT on 2025-03-02, 399 seconds after the Einstein Probe trigger (Dai et al., GCN 39556). Observations were made in partially cloudy conditions. A new and changing source consistent with the XRT position (Page et al., GCN 38761) was detected. We report the following photometric values for the optical transient:

tc-t0(s) g'(mag) err r'(mag) err exposure_time (s) -------------------------------------------------------------- 424 - 18.36 0.08 50 628 - 18.35 0.08 300 928 - 18.80 0.13 300 1273 - 18.76 0.07 240 1513 - 18.55 0.06 240 1753 - 18.12 0.04 240 1993 - 17.71 0.03 240 2233 - 17.58 0.02 240 2686 - 17.48 0.03 240 2926 - 17.54 0.02 240 3166 - 17.58 0.02 240 3406 - 17.65 0.02 240 3646 - 17.68 0.03 240 3886 - 17.73 0.03 240 4126 - 17.85 0.03 240 4366 - 17.88 0.04 240 4606 - 17.95 0.03 240 4846 - 18.08 0.04 240 5086 - 18.11 0.03 240 5326 - 18.18 0.04 240 5566 - 18.32 0.04 240 5806 - 18.47 0.04 240 6046 - 18.56 0.04 240 6348 18.93 0.05 18.56 0.04 240 6588 18.99 0.06 18.76 0.04 240 6828 19.01 0.05 18.86 0.05 240 7068 19.05 0.05 18.86 0.05 240 7308 19.06 0.05 18.90 0.05 240 7548 19.12 0.05 18.94 0.05 240 7788 19.28 0.07 19.01 0.06 240 8028 19.43 0.08 19.01 0.06 240 8269 19.53 0.08 19.19 0.07 240 8509 19.34 0.06 19.19 0.06 240

tc-t0 = trigger time minus image center time. Calibration was done with 4 bright Pan-STARRS catalog stars on our images.

Our results are in agreement with those reported in previously published circulars (Zhu et. al, GCN 39550; Wu et. al, GCN 39555; Xin et. al, GCN 39558; Pankov et al., GCN 39565).

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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