TITLE: GCN CIRCULAR NUMBER: 19166 SUBJECT: GRB 160310A: RATIR Optical and NIR Observations DATE: 16/03/11 14:05:14 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 GRB 160310A (Vianello, et al., GCN 19158; Toelge, et al., GCN 19161) 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 2016/03 11.16 to 2016/03 11.32 UTC (27.46 to 31.25 hours after the GBM trigger). We observed the two uncatalogued X-ray sources detected by the Swift/XRT (Gibson, et al., 19162). For source #1 we obtained a total of 1.07 hours exposure in the r and i bands and 0.45 hours exposure in the J, and H bands. For a source within the XRT error circle, in comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections: r 19.89 +/- 0.02 i 19.34 +/- 0.01 J 18.03 +/- 0.01 H 17.37 +/- 0.01 These values are consistent with the magnitudes of a USNO-B1 catalogued object. No other source is visible within the XRT localization. For source#2 we obtained a total of 1.78 hours exposure in the r and i bands and 0.75 hours exposure in the J, and H bands. For a source within the XRT error circle, in comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections: r 22.48 +/- 0.09 i 21.82 +/- 0.05 J 20.62 +/- 0.10 H 20.03 +/- 0.08 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Our values are slightly fainter than the NOT detection (Kruehler, et al., GCN 19164), although no strong claim about variability can be made at this time. Further observations to determine the nature of source #2 are encouraged. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.