GRB 230506C: NUTTelA-TAO / BSTI Early Optical Limits

The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) observed the field of GRB 230506C, 8 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 17:09:56 UT on 2023-05-06, 37 s after the BAT trigger. Observations were made in cloudy conditions. No source consistent with the XRT (J. A. Kennea et al., GCN Circ. 33736) was detected. We report the following results: start time t-t0(s) end time ULi' exposure_time (s) ------------ ----- ----------- ----- ------ 17:09:56 37 17:10:48 17.4 52.5 17:11:03 104 17:13:33 18.0 150 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. ---------------------------------- NU = Nazarbayev University, Nur-Sultan, 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. AP14870504). 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.