TITLE: GCN CIRCULAR NUMBER: 15274 SUBJECT: GRB 130831A: Continued RATIR Optical and NIR Observations DATE: 13/09/30 16:17:13 GMT FROM: Nat Butler at Az State U William H. Lee (UNAM), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), Nat Butler (ASU), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC), 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 130831A (Hagen, et al., GCN 15139) 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 2013/09 30.12 to 2013/09 30.49 UTC (29.58 to 29.94 days after the BAT trigger), obtaining a total of 6.27 hours exposure in the r and i bands and 2.65 hours exposure in the Z, Y, J, and H bands. For a source within the Swift-XRT error circle (Evans et al., GCN 15147), in comparison with 2MASS, we obtain the following detections and upper limits (3-sigma): r 23.84 +/- 0.18 i 23.23 +/- 0.15 Z > 23.04 Y > 22.53 J > 22.37 H > 21.72 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. The source has faded relative to our last measurement (t~21.5 days; Lee et al., GCN 15242) by about 0.8 magnitudes in r and J and 0.5 magnitudes in i. Our measurements (see, also, Watson et al., GCN 15179; Butler et al., GCN 15165) are consistent with a bump or re-brightening in the lightcurve at t~10 days (see, Pozanenko et al., GCN 15237), followed by continued fading. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.