TITLE: GCN CIRCULAR NUMBER: 19663 SUBJECT: GRB 160705B: RATIR Optical and NIR Observations and Confirmation of the Fading Afterglow DATE: 16/07/06 13:50:49 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Nat Butler (ASU), 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), 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), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report: We observed the field of GRB 160705B (Cannizzo et al., GCN 19657) 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 2016/07 6.17 to 2016/07 6.21 UTC (7.04 to 8.05 hours after the BAT trigger), obtaining a total of 0.66 hours exposure in the r and i bands and 0.30 hours exposure in the Z, Y, J, and H bands. We detect two sources within the enhanced Swift-XRT error circle (Osborne et al., GCN 19659). The brighter source is an uncataloged source at 11:12:26.20 +46:42:01.2 (J2000, +/- 0.5 arcsec) with the following detections and 3-sigma upper limit: r = 22.89 +/- 0.15 i = 22.12 +/- 0.09 Z = 22.34 +/- 0.33 Y = 21.73 +/- 0.32 J > 21.54 H = 20.98 +/- 0.34 The fainter source is a cataloged SDSS source at 11:12:26.42 +46:41:59.6 (J2000, +/- 0.5 arcsec) with the following detections and 3-sigma upper limits: r = 23.39 +/- 0.24 i = 22.61 +/- 0.14 Z = 22.10 +/- 0.26 Y > 21.87 J > 21.54 H > 21.04 These magnitudes are in the AB system, are in comparison with the SDSS DR9 and 2MASS catalogs, and are not corrected for Galactic extinction in the direction of the GRB. We note that Guidorzi et al. (GCN 19658) report an uncataloged source with r of about 21 at 36 minutes after the burst trigger. Their source is only 0.7 arcsec from our brighter uncataloged source and so we postulate that these correspond to the afterglow of the GRB. The afterglow has faded by about 2 magnitudes between their observations at 36 minutes and ours at 7.54 hours, which corresponds to a temporal index of about -0.6. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.