TITLE: GCN CIRCULAR NUMBER: 31285 SUBJECT: GRB 211221A: NUTTelA-TAO / BSTI Early Optical Limits (Preliminary) DATE: 21/12/23 04:17:37 GMT FROM: Toktarkhan Komesh at Nazarbayev University T. Komesh (NU), B. Grossan (UCB, NU), Z. Maksut (NU), M. Krugov (FAI),  E. Linder (UCB, NU), E. Abdikamalov (NU), G. F. Smoot (HKUST, UCB, 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 211221A 19 s after receipt an automated GCN / BAT position alert, observing in Sloan i' band, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We started observations at 20:51:35 UT on 2021-12-21, 175 s after the BAT trigger. Observations were made in clear conditions starting at about 30 deg. target altitude. No source consistent with the XRT (P. Evans et al., GCN Circ. 31275) was detected.  We report the following results: start time    t-t0(s)  end time        ULi'       exposure_time (s) ------------    --------  ------------          ------ -------------------- 20:51:35     175   20:52:35          17.9           60 20:52:50     257   22:12:50          18.4         150 start time is in UT. t-t0(s) gives the time since trigger, in seconds. UL i', gives the 5 sigma upper limit sensitivity in magnitudes, for images co-added to the given exposure time. The first row in the table corresponds to co-adds of an initial short exposure image sequence of 7.5 s. The second row corresponds to co-adds from a continuing series of 15 s exposures.  Calibration was done with the 3 bright Pan-STARRS catalog stars on our images. We caution the reader that these are preliminary results, without color or other corrections. Please also note that times are approximate. ---------------------------------- NU = Nazarbayev University, Nur-Sultan, Kazakhstan UCB = University of California, Berkeley, USA HKUST = Hong Kong University of Science and Technology FAI = Fesenkov Astrophysical Institute, Kazakhstan 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.