TITLE: GCN CIRCULAR NUMBER: 26565 SUBJECT: GRB 191221B: iTelescope optical observations DATE: 19/12/23 00:21:24 GMT FROM: Filipp Dmitrievich Romanov at Amateur astronomer I observed the optical afterglow of GRB 191221B (Laha et al., GCN Circ. 26534) with remote telescope T32 (0.43-m f/6.8 reflector + FLI Proline 16803 CCD) of iTelescope.Net in Siding Spring Observatory (Australia) on 2019-12-22 since 13:28:52 UT (~16.8 hours after the trigger). Two images were obtained in each band with Astrodon luminance filter and Johnson/Cousins V filter for 180 and 120 seconds (Binx2). I detected the optical afterglow in three images in the enhanced Swift-XRT position (Beardmore et al., GCN Circ. 26540); it not present in images from DSS Plate Finder. The following magnitudes (mag. error ~ 0.2) were measured from comparison to nearby stars from APASS DR9 catalogue (Henden et al., 2016): Time of start Exp.time Mag. Comp.star band Filter ---------------------------------------------------------- 13:28:52 UT 180 s 18.1 r' Luminance 13:32:58 UT 180 s 18.3 V V 13:36:51 UT 120 s 18.3 r' Luminance 13:39:46 UT 120 s <17.9 V V ---------------------------------------------------------- Magnitudes were not corrected for Galactic extinction.