GRB 241218A: NUTTelA-TAO / BSTI Optical Limits

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