TITLE: GCN CIRCULAR NUMBER: 16387 SUBJECT: GRB 140606B / iPTF 14bfu: MOSFIRE NIR imaging DATE: 14/06/12 02:11:11 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech), M. Kasliwal (Carnegie), L. P. Singer, Y. Cao (Caltech), and K. Tinyanont (Harvey Mudd) report: Beginning at 12:57 UT on 2014-06-08 we observed the field of iPTF14bfu (Singer et al., GCN 16360), the optical counterpart of GRB 140606B (Burns et al., GCN 16363), using the imaging mode of MOSFIRE on the Keck I 10m telescope. A sequence of nine 23-second images was acquired in the Ks filter. Calibrating relative to 2MASS stars in the image, we measure a magnitude of: Ks = 19.50 +/- 0.06 (Vega, or Ks = 21.34 AB) at a mid-time of 2.411 days after the initial trigger. We also measure an improved astrometric position (relative to 2MASS) of: 21:52:29.961 +32:00:50.66 (J2000, +/- 0.2")