TITLE: GCN CIRCULAR NUMBER: 23089 SUBJECT: GRB 180805B: COATLI Optical Observations DATE: 18/08/06 17:18:16 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Carlos Román-Zúñiga (UNAM), Alexander Kutyrev (GSFC), and Eleonora Troja (GSFC) report: We observed the field of the short GRB 180805B (D'Avanzo et al., GCN Circ. 23076) with the COATLI 50-cm telescope and interim imager at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir (http://coatli.astroscu.unam.mx) from 2018-08-06 08:01 to 11:48 UTC (18.98 to 22.77 hours after the trigger), obtaining a total of 2.98 hours of exposure in the w filter. We do not detect any optical sources within the enhanced XRT error region (Evans et al., GCN Circ. 23077) to a 5-sigma limiting magnitude of w > 22.5 This magnitude is calibrated against the USNO-B1 catalog (adjusted to an approximate AB system) and is not corrected for Galactic extinction in the direction of the GRB. We thank the COATLI technical team (Fernando Ángeles, Oscar Chapa, Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosalía Langarica, Fernando Quirós, and Carlos Tejada) and the staff of the Observatorio Astronómico Nacional.