TITLE: GCN CIRCULAR NUMBER: 27564 SUBJECT: GRB 200412B: Optical afterglow detection with 1.3m DFOT DATE: 20/04/13 09:14:18 GMT FROM: Amit Kumar at ARIES, India TITLE: GCN CIRCULAR NUMBER: 27563 SUBJECT: GRB 200412B: Optical afterglow detection with 1.3m DFOT DATE: 20/04/13 09:05:41 GMT FROM: Amit Kumar at ARIES, India A. Kumar (ARIES), A. Aryan (ARIES), S. B. Pandey (ARIES), S. Mishra (ARIES), R. Gupta (ARIES), A. Ghosh (ARIES), Dimple (ARIES), and K. Misra (ARIES) report: We observed the optical afterglow of the Fermi GBM detected GRB 200412B (GCN 27547, Lipunov et al., GCN 27555, GCN 27561) with the 1.3m Devsthal Fast Optical Telescope (DFOT) at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital (India), from 2020-04-12 UT 22:03:14 to 2020-04-12 UT 23:29:44 (corresponding to 12.90 to 14.46 hours from the GRB trigger time). We observed a series of 9x300s exposures in Bessel R filter and a series of 7x360s exposures in Bessel I filter. We stacked the images and detected the optical afterglow of GRB 200412B in both Bessel R and I filters which is consistent with optical detections by Lipunov et al., GCN 27555, 27556. The observed magnitudes are as follows: T_start-T0 (hours) Start Date (UTC) End Date (UTC) Filter Magnitudes --------------------------------------------------------------------------------------------------------------- 12.90 2020-04-12 UT 22:03:14 2020-04-12 UT 22:46:11 R 18.90 +- 0.03 13.72 2020-04-12 UT 22:52:02 2020-04-12 UT 23:29:44 I 17.54 +- 0.02 Photometry is done based on the USNO-B1.0 catalog. The quoted magnitudes are not corrected for Galactic extinction.