TITLE: GCN CIRCULAR NUMBER: 15525 SUBJECT: GRB 131127A: RATIR Optical and NIR Observations, High-z Candidate DATE: 13/11/28 08:41:53 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 131127A (Markwardt, et al., GCN 15516) 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 2013/11 28.11 to 2013/11 28.26 UTC (16.42 to 19.94 hours after the BAT trigger), obtaining a total of 2.49 hours exposure in the r and i bands and 1.04 hours exposure in the Z, Y, J, and H bands. We do not detect any sources within the Enhanced Swift-XRT error circle (Evans et al., GCN 15520), in comparison with 2MASS, we obtain the following upper limits (3-sigma): r > 24.19 i > 23.53 Z > 22.78 Y > 22.16 J > 22.04 H > 21.48 However, we do detect a red source just outside (3.3" away from the center) of the XRT position, at a position RA, DEC = 332.731227 , 36.609171 (J2000, +/- 0.5"). We measure: r = 24.21 +/- 0.35 i = 22.48 +/- 0.11 Z = 21.85 +/- 0.16 Y = 21.22 +/- 0.15 J = 21.03 +/- 0.14 H = 20.88 +/- 0.20 The faint flux in r band relative to the redder bands could be due to IGM attenuation at high redshift, z ~ 5. We cannot confirm fading of this source. Further observations of this source are encouraged. The magnitudes above are in the AB system and are not corrected for Galactic extinction, E[B-V]~0.1, in the direction of the GRB. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.