TITLE: GCN CIRCULAR NUMBER: 31704 SUBJECT: GRB 220306B: BOOTES-1 optical upper limit DATE: 22/03/07 15:18:18 GMT FROM: Youdong HU at IAA-CSIC Y.-D. Hu, E. Fernandez-Garcia, T.-R. Sun, A. J. Castro-Tirado (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco, A. Reina (Univ. de Malaga) and F. Rendon (IAA-CSIC and INTA-CEDEA) on behalf of a larger collaboration, report: Following the detection of GRB 220306B by Swift (Caputo et al., GCNC 31697) and Fermi (Wood et al., GCNC 31702), the 0.3m BOOTES-1B robotic telescope in Mazagon (Huelva), southern Spain, automatically responded to this burst on Mar 7 at 00:05 UT (~5.8 hours after trigger). In the co-added frame (20 x 60 s, clear filter), no source is detected within the enhanced XRT position (Evans et al., GCNC 31700) down to 18.5 mag, which is consistent with the non-detections reported by UVOT (Caputo et al., GCNC 31697) and MASTER (Lipunov et al., GCNC 31699). We thank the staff at INTA-CEDEA for their excellent support.