TITLE: GCN CIRCULAR NUMBER: 31023 SUBJECT: GRB 211023A: 1.3m DFOT Optical Observations DATE: 21/10/30 07:13:38 GMT FROM: Rahul Gupta at ARIES, India <rahulbhu.c157@gmail.com> [image: image.gif]Amit Kumar, Rahul Gupta, Amit Ror, Dimple, Ankur Ghosh, Arpan Ghosh, Amar Aryan, Brajesh Kumar, S. B. Pandey, and Kuntal Misra (ARIES) report: We observed the Fermi GBM and LAT detected GRB 211023A (Fermi GBM Team, GCN 30958; Lesage et al. 2021, GCN 30965; and N. Di Lalla et al. 2021, GCN 30961) with 1.3m Devasthal Fast Optical Telescope (DFOT) located at Devasthal observatory of Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2021-10-28 at 19:22:54 UT, i.e., ~ 5.26 days after the Fermi trigger. We have taken multiple frames having an exposure time of 300 sec in the R filter. We clearly detected the optical afterglow of GRB 211023A (Lipunov et al. 2021, GCN 30970; Zhirkov et al. 2021, GCN 30977; Kann et al. 2021, GCN 30982; Hu et al. 2021, GCN 30990; Belkin et al. 2021, GCN 31004, 31018, 31020; and Vinko et al. 2021, GCN 31008) in our stacked image. The preliminary photometric estimate of the afterglow is the following : Date Start UT T-T0 (mid, days) Filter Exp time (sec) Magnitude ========================================================= 2021-10-28 19:22:54 ~5.28 R 300*15 21.37 +/- 0.08 Further observations are requested with 1.3m DFOT.The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog. This circular may be cited.