GCN Circular 4110
J. S. Bloom (UCB), H.-W. Chen, (Chicago), R. J. Foley (UCB), J. X. Prochaska (UCSC), report on behalf of a larger collaboration: "We observed the position of GRB 051016b (GCN 4103) with the NIRI instrument on the Gemini North Telescope beginning 20051017.59 UTC. In a stack of 45 minutes of exposure we detect several faint sources consistent with the XRT position (GCN 4108): A: 08:48:27.85 13:39:20.4 B: 08:48:27.32 13:39:18.1 C: 08:48:27.64 13:39:13.6 D: 08:48:27.42 13:39:23.9 The astrometry is derived assuming the nominal platescale of NIRI and based on the assumption that a bright galaxy (2MASS 1036.075258) is at position (J2000) 08:48:27.607 +13:39:02.67. Source A is 0.6" E and 0.4" N of an optical source reported by Maeno et al. (GCN 4106) and we thus associate this apparent IR point source (A) with the Lulin/UVOT source. We measure an isophotal mag of Ks[A] = 20.52 +/- 0.12 mag, assuming the 2MASS galaxy has magnitude of Ks = 15.209 mag. We make no claim of variability but source A is the most point-like of the 4 objects in the XRT error circle, so it is still a plausible afterglow candidate." We thank the Gemini observing staff for performing this ToO. This message may be cited.