TITLE: GCN CIRCULAR NUMBER: 18140 SUBJECT: GRB 150811A: Continued RATIR Observations DATE: 15/08/13 19:28:24 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 150811A (Evans, et al., GCN 18119) 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 2015/08 13.14 to 2015/08 13.40 UTC (47.37 to 53.59 hours after the BAT trigger), obtaining a total of 4.93 hours exposure in the r, i, and z bands. We continue to detect the optical afterglow. Relative to the flux reported in Butler et al. (GCN 18132), the source continues to appear to fade approximately as t^(-1). In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections and upper limit (3-sigma): r = 22.00 +/- 0.20 i = 21.83 +/- 0.20 z > 20.40 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.