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GCN Circular 4110

GRB 051016b: Gemini Near IR Observations
2005-10-18T08:07:33Z (19 years ago)
Ryan Foley at UC Berkeley <>
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.

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