TITLE: GCN CIRCULAR NUMBER: 17343 SUBJECT: GRB 150120B: RATIR Optical and NIR Observations DATE: 15/01/21 21:24:35 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), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report: We observed the field of GRB 150120B (D'Elia, et al., GCN 17314) 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 2015/01 21.09 to 2015/01 21.29 UTC (18.73 to 23.64 hours after the BAT trigger), obtaining a total of 3.91 hours exposure in the r, i, and z bands. For a source coincident with the GROND optical transient (Wiseman et al., GCN 17336), in comparison with 2MASS, we obtain the following detections and upper limit (3-sigma): r = 23.4 +/- 0.2 i = 22.6 +/- 0.1 z > 20.72 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.