TITLE: GCN CIRCULAR NUMBER: 38611 SUBJECT: GRB 241218A: NUTTelA-TAO / BSTI Optical Limits DATE: 24/12/18 10:05:41 GMT FROM: Zhanat Maksut at Nazarbayev University zhanat.maksut@nu.edu.kz

Z. Maksut (NU), B. Grossan (UCB, NU), T. Komesh (NU), Z. Abdullayev (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) observed the field of GRB 241218A, 12 seconds after receipt of an automated GCN / BAT position alert, in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (Grossan, Kumar & Smoot 2019, JHEA, 32, 14).

We started observations of GRB 241218A (Williams et al., GCN 38601; Strausbaugh et al., GCN 38605) at UT 00:13:43 on 2024-12-18, 292 seconds after the BAT trigger. Observations were made in clear conditions. We report the following upper limit results:

start time t_m-t0(s) end time UL g' UL r' exposure_time (image x s) ----------------------------------------------------------------------- 00:26:30 1191 00:29:30 19.51 19.57 3 x 60

The start and end time is in UT. t_m is the middle time, t0 is the BAT trigger time, t_m-t0 is given in seconds. UL gives the 5 sigma upper limit sensitivity in magnitudes, for images co-added to the given exposure time. Calibration was done with 4 Pan-STARRS catalog stars on our images. No color corrections were applied to the values above.

---------------------------------- NU = Nazarbayev University, Astana, Kazakhstan UCB = University of California, Berkeley, USA FAI = Fesenkov Astrophysical Institute, Kazakhstan

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