TITLE: GCN CIRCULAR NUMBER: 29599 SUBJECT: GRB 210306A: iTelescope optical afterglow observations DATE: 21/03/06 05:53:48 GMT FROM: Filipp Dmitrievich Romanov at Amateur astronomer I observed the field of GRB 210306A (D'Elia et al., GCN Circ. 29597) with remote telescope T24 (0.61-m f/6.5 reflector + CCD) of iTelescope.Net in Sierra Remote Observatory (Auberry, California, USA) on 2021-03-06. Two images (exposures 300 seconds, BINx1) were obtained with luminance filter since 04:42:56 UT (2939 seconds after the trigger) and since 04:48:59 UT (3302 seconds after the trigger). I clearly detected the optical afterglow in UVOT position. The following magnitudes were measured from comparison to r magnitudes of nearby stars from Pan-STARRS DR1 catalogue (Chambers et al., 2016): 17.80 (+/- 0.057) and 17.97 (+/- 0.038). Magnitudes were not corrected for Galactic extinction. Stacked image available here: https://www.flickr.com/photos/filipp-romanov/51007330278