TITLE: GCN CIRCULAR NUMBER: 29173 SUBJECT: GRB 201223A: 1.3m DFOT and 1.04m ST optical observations DATE: 20/12/24 17:09:51 GMT FROM: Rahul Gupta at ARIES, India Rahul Gupta (ARIES), Dimple (ARIES), Amit Kumar (ARIES), Vineet Ojha (ARIES), Ankur Ghosh (ARIES), Amar Aryan (ARIES), Shashi B. Pandey (ARIES), and Kuntal Misra (ARIES) report: We observed the optical afterglow ( Lipunov et al., GCN 29157; Gropp et al., GCN 29158; Zhu et al., GCN 29159; Hu et al., GCN 29160; Hosokawa et al., GCN 29164; Romanov et al., GCN 29165; Xin et al., GCN 29166; Belkin et al., GCN 29167; and Kumar et al., GCN 29168) of Swift and Fermi detected GRB 201223A (Gropp et al., GCN 29158; and Wood et al., GCN 29161) using the 1.3m Devasthal Fast Optical Telescope (DFOT) and 1.04m Sampurnanand Telescope (ST) of Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2020-12-23 at 19:01:46 UT. Multiple frames having an exposure time of 300 s were taken in the I filter using DFOT and in BVRI filters using ST. We clearly detected the optical counterpart at the position reported by Gropp et al., GCN 29158. The preliminary photometric estimate of the afterglow using I band data of DFOT is the following : Date Start_UT T_start-T0 (hrs) Filter Exp time (s) Magnitude Mag_err ------------------------------ ------------------------------ ------------------------------ ------------------------------ 2020-12-23 19:07:55 1.158 I 300*1 18.71 0.04 ------------------------------ ------------------------------ ------------------------------ ------------------------------ The magnitude is not corrected for the Galactic and Host extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. Further processing of data is going on. This circular may be cited.