TITLE: GCN CIRCULAR NUMBER: 34853 SUBJECT: GRB 231017A: 1.3m DFOT Optical upper limit DATE: 23/10/20 17:12:08 GMT FROM: Amit Kumar Ror at ARIES <mitturor77894@gmail.com> Amit K. Ror, Rahul Gupta, Amar Aryan, Shashi B. Pandey, Rishi C., and Neelam Panwar (ARIES) report: We observed the field of Fermi, and Swift detected GRB 231017A (Fermi GCM Team GCN 34822; Mangan et al. 2023, GCN 34830; DeLaunay et al. 2023, GCN 34824; and Swift team GCN 34825) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2023-10-18 at 22:19:07 UT, i.e., ~ 1.6 days after the GBM trigger. We have taken multiple frames with an exposure time of 100 s in the R filter. We stacked the images after the alignment. We did not detect any optical afterglow in our stacked image within the error box of Swift-XRT observation (Dichiara et al., 2023, GCN 34829). We obtain the following preliminary 3-sigma upper limit in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Limiting magnitude ========================================================= 2023-10-18 22:19:07 1.6 R 100*36 > 21.6 Our non-detection is consistent with Kumar et al. 2023, GCN 34833; Strausbaugh et al. 2023, GCN 34834; Shrestha et al. 2023, GCN 34836; Xu et al. 2023, GCN 34840; and Belkin et al. 2023, GCN 34841. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/34853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...