TITLE: GCN CIRCULAR NUMBER: 23204 SUBJECT: GRB 180904A: RATIR Optical and NIR Observations DATE: 18/09/05 15:49:17 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report: We observed the field of GRB 180904A (D'Ai, et al., GCN 23194) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2018/09 5.13 to 2018/09 5.32 UTC (5.66 to 10.26 hours after the BAT trigger), obtaining a total of 2.91 hours exposure in the r and i bands and 1.33 hours exposure in the Z, Y, J, and H bands. Within the XRT error circle (Osborne, et al., GCN 23196), we detect the source reported by Malesani, et al. (GCN 23195) at a consistent brightness level. In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections and upper limit (3-sigma): r = 22.61 +/- 0.08 i = 22.06 +/- 0.05 Z = 22.13 +/- 0.16 Y = 21.64 +/- 0.18 J = 21.72 +/- 0.21 H > 21.86 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.