TITLE: GCN CIRCULAR NUMBER: 20485 SUBJECT: LIGO/Virgo G268556: RATIR Observation of iPTF Candidates DATE: 17/01/20 05:10:34 GMT FROM: V. Zachary Golkhou at ASU/SESE--RATIR Zach Golkhou (ASU), Nat Butler (ASU), Neil Gehrels (GSFC), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Eleonora Troja (GSFC), and Alan M. Watson (UNAM) report: We observed a number of iPTF candidates (Kasliwal et al. LVC GCN#20398) 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 2017/01 11.28--11.30 UTC (6.85 days since the GW trigger; Shawhan et al. LVC GCN #20364) and again from 2017/01 12.44--12.46 UTC. At positions consistent with each iPTF source position, we report riZY photometry for the probable host galaxy from the first epoch. In comparison with the SDSS DR9 and 2MASS catalogs, we obtain: # Source r (dt_r) i (dt_i) Z (dt_Z) Y (dt_Y) iPTF17ce 19.84+/-0.04 (0.36) 18.92+/-0.02 (0.36) 18.37+/-0.02 (0.07) 18.35+/-0.03 (0.07) iPTF17ck 18.17+/-0.01 (0.71) 17.59+/-0.01 (0.71) 17.63+/-0.01 (0.15) 17.33+/-0.01 (0.15) iPTF17dz ... 19.09+/-0.01 (0.51) 19.30+/-0.03 (0.22) 19.23+/-0.04 (0.22) iPTF17ef 19.18+/-0.02 (1.07) 18.92+/-0.02 (1.07) 18.86+/-0.03 (0.22) 18.59+/-0.02 (0.22) iPTF17ei 16.77+/-0.01 (1.38) 16.37+/-0.01 (1.38) 16.17+/-0.01 (0.29) 15.97+/-0.01 (0.29) These magnitudes are in the AB system and are not corrected for Galactic extinction in the source direction. Exposure times (dt) are reported in hours. We find no evidence for variation in flux at >2-sigma confidence from an image subtraction analysis between our two epochs. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.