TITLE: GCN CIRCULAR NUMBER: 10909 SUBJECT: GRB 100628A: Gemini North Observations DATE: 10/06/29 17:46:37 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan (U. Warwick), N.R. Tanvir, K. Wiersema (U. Leicester), S.B. Cenko (UC Berkeley) report on behalf of a larger collaboration: "We obtained two epochs of observations of GRB 100628A (Immler et al. GCN 10895) with Gemini-North. The first was obtained starting at 28 Jun, 08:59 UT, approximately 43 minutes after the burst, with a second obtained on 29 Jun 05:50 UT, ~21.5 hours after the burst. A total of 1200s of exposure time were obtained in the i-band. Our images covers ~90% of the BAT refined error circle (Barthelmy et al GCN 10896), including the position of the candidate X-ray afterglow identified by Starling et al. (GCN 10899; 10907). Digital image subtraction performed between the two epochs does not reveal any candidate variable sources between the two epochs, to an approximate limiting magnitude of i~24. In particular, we do not find any evidence for variability in any of the galaxies identified by Berger et al. (GCN 10902) surrounding the XRT location, including G1, which now lies within the XRT error circle (Starling et al. GCN 10907; Berger et al. GCN 10908) We also note the presence of two, apparently point like sources lying within the refined XRT error circle, at locations of S1: RA(J2000) 15:03:53.45 DEC(J2000) -31:39:54.2 S2: RA(J2000) 15:03:53.73 DEC(J2000) -31:39:48.4 Both are unresolved at the resolution of our observations, but neither show apparent variability between the two epochs. An image, showing the field as observed by Gemini-North can be found at http://www.star.le.ac.uk/~anl/100628A We thank the staff of Gemini-North for their assistance with these observations."