TITLE: GCN CIRCULAR NUMBER: 19588 SUBJECT: GRB 160625B: RATIR Optical and NIR Afterglow Detection DATE: 16/06/26 08:18:57 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), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (GSFC/STScI), 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), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report: We observed the field of the Fermi LAT GRB 160625B (Dirirsa, et al., GCN 19580) 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 2016/06 26.30 to 2016/06 26.32 UTC (8.53 to 9.02 hours after the LAT trigger), obtaining a total of 0.36 hours exposure in the r and i bands and 0.15 hours exposure in the Z, Y, J and H bands. We detect a bright, fading and uncatalogued source at the edge of the Swift-XRT error circle (Melandri, et al., GCN 19585), at a position RA, Dec = 20:34:23.50, +6:55:8.1 (J2000, +/-0.5"). In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following values: r = 18.28 +/- 0.01 i = 18.08 +/- 0.01 Z = 17.95 +/- 0.01 Y = 17.78 +/- 0.01 J = 17.77 +/- 0.02 H = 17.65 +/- 0.02 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Further observations are on-going. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.