TITLE: GCN CIRCULAR NUMBER: 12387 SUBJECT: GRB 110921A: NOT observations DATE: 11/09/22 16:11:30 GMT FROM: Paul Vreeswijk at U of Iceland Paul Vreeswijk (U. Iceland), Daniele Malesani, Antonio de Ugarte Postigo (DARK, NBI), Dong Xu (WIS), Páll Jakobsson, Steve Schulze (U. Iceland) and Nial Tanvir (U. Leicester) report on behalf of a larger collaboration: Using ALFOSC on the Nordic Optical Telescope (NOT) we have obtained Sloan r'- (3 x 600 s) and z'-band (6 x 300 s) imaging of the field of GRB 110921A (Baumgartner et al., GCN 12373, Barthelmy et al., GCN 12383), starting on 2011 September 21.925 UT (roughly 8.3 hr after the burst). The observations were performed through clouds, but under good seeing conditions (~0.8"). We do not detect the optical afterglow reported by Xin et al. (GCN 12377, see also Xu et al., GCN 12385), or any other object within the enhanced Swift-XRT error circle (Goad et al., GCN 12379), down to limiting magnitudes of about r'=23.3 and z'=21.0 (calibrated against the SDSS catalog). Just outside the enhanced XRT error circle, at R.A.(J2000) 19:36:23.38, decl.(J2000) 36:19:42.1 (with an uncertainty of 0.23"), we detect an r'=22.4+-0.2 source, also visible - albeit barely - in the combined z'-band imaging. This apparent point source is consistent, both in position and brightness, with the SDSS object noted by Xu et al. (GCN 12385). We are grateful for the NOT staff, particularly Fatemeh Sadat Kiaeerad and Marjaana Lindborg, for obtaining these observations.