TITLE: GCN CIRCULAR NUMBER: 29539 SUBJECT: GRB 210217A: 1.3m DFOT optical detection DATE: 21/02/19 19:32:22 GMT FROM: Amit Kumar at ARIES, India Amit Kumar (ARIES), Rahul Gupta (ARIES), Ankur Ghosh (ARIES), Dimple (ARIES), Tushar Tripathi (ARIES), Shubham Kishore (ARIES), Amar Aryan (ARIES), Shashi B. Pandey (ARIES), Brajesh Kumar (ARIES), and Kuntal Misra (ARIES) report: We observed the optical afterglow of the Swift detected GRB 210217A (Simpson et al. GCN 29521; Evans et al., GCN 29525) with the 1.3m Devsthal Fast Optical Telescope (DFOT) at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital (India), on 2021-02-18 from UT 17:31:22 to 19:09:31 (corresponding to 18.094 to 19.730 hours from the GRB trigger time). We observed a series of 30x120s exposures in the Bessel R filter and a series of 20x120s exposures in the Bessel I filter. We clearly detected the optical afterglow of GRB 210217A in the stacked frames within the Swift XRT error circle (Simpson et al. GCN 29521) as also reported by Zhu et al., GCN 29523; Zheng & Filippenko GCN 29533; Shrestha et al. GCN 29535. The estimated preliminary magnitudes are as follows: T_start-T0 (hours) Start Date (UTC) Filter Magnitude (mag) ----------------------------------------------------------- ----------------------------------------------------------- 18.09 2021-02-18T17:31:22 R 21.80 +- 0.08 19.73 2021-02-18T19:09:31 I 21.56 +- 0.12 The magnitudes are 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.