TITLE: GCN CIRCULAR NUMBER: 32880 SUBJECT: GRB 221027B: COATLI Upper Limits DATE: 22/10/28 18:36:57 GMT FROM: Rosa Leticia Becerra Godinez at Inst. de Astronoma,UNAM Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU), Simone Dichiara (PSU), Tzveti Dimitrova (ASU), Océlotl López (UNAM), Diego González (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Margarita Pereyra (UNAM), Eleonora Troja (UTV/ASU) and report: We observed the field of the GRB 221027B (Lien et al., GCN Circ. 32867) with the COATLI 50-cm telescope and HUITZI f/8 imager at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir ( http://coatli.astroscu.unam.mx) from 2022-10-28 01:47 UTC to 02:13 UTC (6.6 hours after the trigger), obtaining a total of 750 seconds of exposure in the r filter. We do not detect any uncataloged sources within the XRT error region (Beardmore et al., GCN Circ. 32868) to a 3-sigma limit of r > 21.4 mag. Our photometry is calibrated against the Pan-STARRS1 catalog, is on an approximate AB system, and is not corrected for Galactic extinction in the direction of the GRB. We thank the COATLI/HUITZI technical team and the staff of the Observatorio Astronómico Nacional.