TITLE: GCN CIRCULAR NUMBER: 35483 SUBJECT: GRB 240101B: 1.3m DFOT optical upper limit DATE: 24/01/05 11:17:13 GMT FROM: Amit Kumar Ror at ARIES <mitturor77894@gmail.com> Amit K. Ror, Rahul Gupta, Amar Aryan, and Shashi B. Pandey (ARIES) report: We observed the field of the GRB 240101B detected by Swift (Cenko et al. 2024, GCN 35449) 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 2024-01-02 at 12:43:55 UT, i.e., ~ 0.68 days after the BAT trigger. We have taken multiple frames with an exposure time of 300 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 enhanced Swift-XRT error box (Evans et al., 2024, GCN 35455). 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 ========================================================= 2024-01-02 12:43:55 ~0.68 R 300*12 > 21.7 Our non-detection is consistent with Zheng et al. 2024, GCN 35454; Kuin et al. 2024, GCN 35458; and Peretto 2024, GCN 35463. 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/35483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...