TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4216 SUBJECT: GRB 051109a: IR Photometry and Astrometry DATE: 05/11/09 04:17:16 GMT FROM: Josh Bloom at UC Berkeley J. S. Bloom (UC Berkeley), C. H. Blake (Harvard), D. Starr (Gemini) and K. Alatalo (UC Berkeley) report: "We have continued to observe the field of GRB 051109a (Tagliaferri et al. 4213) at the position of the optical transient (GCNs 4211, 4214, 4215). Using a stack of PAIRITEL imaging from 2005-11-09 01:18:42.25 to 2005-11-09 01:33:14.94 UTC we find a 2MASS calibrated photometry of J = 15.69 +/- 0.03, H = 14.95 +/- 0.03, Ks = 14.44 +/- 0.04. We also find an astrometric position of (J2000) 22:01:15.313, +40:49:23.31 with an uncertainty of 100 mas in each axis. This is consistent with the Rykoff et al. position." This message may be cited