TITLE: GCN CIRCULAR NUMBER: 22631 SUBJECT: GRB 180410A: RATIR Optical Observations DATE: 18/04/11 16:03:38 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Nat Butler (ASU), 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 180410A (Gropp et al., GCN 22620) 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 2018/04 11.13 to 2018/04 11.25 UTC (19.10 to 21.87 hours after the BAT trigger), obtaining a total of 2.13 hours exposure in the r and i bands. For a source within the Swift-XRT error circle, in comparison with the USNO-B1 and 2MASS catalogs, we obtain the following upper limits (3-sigma): r > 24.20 i > 23.90 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. The XRT error region is only 2.8 arcsec from a previously cataloged star with r = 18.1 and i = 17.4. Thus, our formal upper limits given above may be optimistic. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.