TITLE: GCN CIRCULAR NUMBER: 14684 SUBJECT: GRB 130518A: Continued RATIR Optical Observations - Fading DATE: 13/05/20 15:30:09 GMT FROM: Eleonora Troja at GSFC Eleonora Troja (GSFC), 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 (UCSC), 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 again observed the field of GRB 130518A (Xiong, et al., GCN 14674; Omodei, et al., GCN 14675) 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 2013/05 20.43 to 2013/05 20.46 UTC (44.41 to 45.24 hours after the GBM trigger), obtaining a total of 0.71 hours exposure in the r' and i' bands. In comparison with SDSS DR8, we obtain the following detections of the source reported earlier (Troja, et al., GCN 14678; Cenko, GCN 14680): r' 20.47 ± 0.04 i' 20.19 ± 0.04 These magnitudes are in the AB system and not corrected for Galactic extinction in the direction of the GRB. In comparison with our earlier observations (Troja, et al., GCN 14678), the source has faded by slightly more than 1 magnitude in r' and i' between about 21 hours and 45 hours after the trigger. This confirms that the source corresponds to the afterglow of GRB 130518A. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.