TITLE: GCN CIRCULAR NUMBER: 35830 SUBJECT: GRB 240225B: 3.6m DOT observation DATE: 24/02/29 06:15:59 GMT FROM: Amit Kumar Ror at ARIES <mitturor77894@gmail.com> Amit K. Ror, Shashi B. Pandey, Rahul Gupta, and Amar Aryan, Shivangi Pandey (ARIES) report: We observed the field of GRB 240225B detected by MAXI (Nakajima et al. 2024, GCN 35796), Swift (Evans 2024, GCN 35797), and AstroSat (Joshi et al. 2024, GCN 35798) using the 3.6m Devasthal Optical Telescope of ARIES Nainital. The observations were started on 2024-02-28 at 01:04:01.085 UT, i.e., 2.2 days after the MAXI trigger. We have taken multiple frames with a 60-second exposure time in the r, i, and z filters. We detected the OT at the position of the GOTO afterglow candidate reported by Gompertz et al. (2024, GCN 35805) in each observed image in the i and z bands and the stacked image of the r band, indicating a redder nature. The preliminary magnitude measurements are as follows: Date Start_UT T_start-T0 (days) Filter Exp time (s) Limiting magnitude ========================================================= 2024-02-28 01:04:01.085 2.2 i 60s 19.96 +/- 0.04 Our i-band observation, combined with the observation of Wise et al. (2024, GCN 35820), yielded a decay index of ~ 0.8 in the i-band. The magnitude quoted is not corrected for the host and Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the Pan-STARRS catalog. Our detection is consistent with Gompertz et al. 2024, GCN 35805; Liu et al. 2024, GCN 35812; Malesani et al. 2024, GCN 35819; Wise et al. 2024, GCN 35820; Gompertz et al. 2024, GCN 35824; Pankov et al. 2024, GCN 35826; Moskvitin et al. 2024, GCN 35828; and Geoffrey et al. 2024, GCN 35829. This circular may be cited. 3.6m Devasthal Optical Telescope (DOT) is a recently commissioned facility in the Northern Himalayan region of India (long:79 41 04E, lat:29 21 40N, alt:2540m) owned and operated by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital ( https://www.aries.res.in). Authors of this GCN circular thankfully acknowledge consistent support from the staff members to run and maintain the 3.6m DOT. View this GCN Circular online at https://gcn.nasa.gov/circulars/35830. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...