TITLE: GCN CIRCULAR NUMBER: 22614 SUBJECT: GRB 180407A: COATLI Upper Limits DATE: 18/04/07 04:37:08 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 GRB 180407A (Deich et al., GCN 22612) with the COATLI 50-cm telescope and interim imager (http://coatli.astroscu.unam.mx) at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir from 2018-04-07 02:26:12 to 03:01:38 (0.52 to 1.12 hours after trigger) obtaining a total of 510 seconds of exposure in the w filter. The images were obtained at high airmass (above 3.1) and during twilight. For a source within the Swift/BAT error circle, in comparison with the USNO-B1 catalog, we obtain the following 10-sigma upper limit: w > 16.53 This magnitude is in the USNO 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. -- Dr. Alan M. Watson Instituto de Astronomía Universidad Nacional Autónoma de México