TITLE: GCN CIRCULAR NUMBER: 39115 SUBJECT: GRB 250129A: 1.3m DFOT Optical observations DATE: 25/02/01 17:07:56 GMT FROM: Amit Kumar Ror at ARIES <mitturor77894@gmail.com> Amit K. Ror, Anshika Gupta, Kiran, Shashi B. Pandey, Kuntal Mishra (ARIES) report: We observed the field of GRB 250129A detected by the Swift Burst Alert Telescope (Swift team, Beardmore et al. 2025; GCN 39066) 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 2025-01-30 at 22:57:11 UT, i.e., ~ 1.76 days after the Swift-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 detected an optical afterglow in our stacked image within the error box of the enhanced Swift-XRT position by Goad et al. 2025 (GCN 39082). Further observations of the burst are still ongoing. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ========================================================= 2025-01-30 22:57:11 ~1.76 R 300s*12 19.52 +/- 0.03 Our detection is consistent with Francile et al. 2025 (GCN 39065); Lipunov et al. 2025 (GCN 39070); Schneider et al. (GCN 39071); Belkin et al. 2025 (GCN 39072); Izzo et al. 2025 (GCN 39073); Izzo et al. 2025 (GCN 39074); Francile et al. 2025 (GCN 39075); Ghosh et al. 2025 (GCN 39077); Schneider et al. 2025 (GCN 39078); Brivio et al. 2025 (GCN 39079); Siegel et al. 2025 (GCN 39085); Zheng et al. 2025 (GCN 39090); Schlekat et al. 2025 (GCN 39091); Antier et al. 2025(GCN 39096); Odeh et al. 2025 (GCN 39097); Ferro et al. 2025(GCN 39098); Bochenek et al. 2025 (GCN 39099);Malesani et al. 2025 (GCN 39100); Romanov et al. 2025 (GCN 39101); Zheng et al. 2025 (GCN 39102); Zheng et al. 2025 (GCN 39102); Watson et al. 2025 (GCN 39104); Vinko et al. 2025(GCN 39105); Akl et al. 2025 (GCN 39106); Moskvitin et al. 2025 (GCN 39107); Giovanni et al. 2025 (GCN 39109); Schlekat et al. 2025 (GCN 39110) and Schlekat et al. 2025 (GCN 39114). 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 catalogue. This circular may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39115. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...