TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4749 SUBJECT: GRB 050826: Optical Afterglow and Host Galaxy DATE: 06/02/12 01:53:14 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report on behalf of the MDM Observatory GRB follow-up team: "Follow-up observations summarized here support our original suggestion in GCN 3891 of an optical afterglow for the Swift GRB 050826 (GCN 3884, 3888), and indicate the presence of a relatively bright host galaxy for this long burst. First, the Swift XRT position of the afterglow, which was originally determined to lie 8" from the optical candidate with an 90% uncertainty radius of 6" (GCN 3889, 3891), was subsequently refined (as were all XRT positions). In the revised catalog of Moretti et al. (astro-ph/0511604), the XRT position falls only 3.1" from the optical position, consistent with the improved 3.4" X-ray uncertainty. --------------------------------------------------- R.A. (2000) Dec. (2000) +/- (") --------------------------------------------------- Swift XRT 05 51 01.49 -02 38 38.6 3.4 MDM 1.3m OT 05 51 01.58 -02 38 35.8 0.5 MDM 2.4m host 05 51 01.59 -02 38 36.2 0.5 --------------------------------------------------- Second, image subtraction among observations obtained on three consecutive nights on the MDM 1.3m reveals a point-like OT on the first night only, and shows that the light is dominated by the host galaxy on the second and third nights. The OT is offset ~0.4" to the north of the brightest part of the galaxy. ------------------------------------------------------ MDM 1.3m ------------------------------------------------------ Date(UT) Time(UT) t-t0(hours) Diff OT R(mag) ------------------------------------------------------ Aug. 26 10:42-11:57 4.40- 5.65 22.23 +/- 0.15 Aug. 27 10:43-11:58 28.42-29.67 > 22.8 Aug. 28 11:03-11:57 52.75-53.65 ------------------------------------------------------ MDM 2.4m Host R(mag) ------------------------------------------------------ Dec. 25 21.67 +/- 0.05 ------------------------------------------------------ Third, using the MDM 2.4m, RETROCAM imager, and SDSS r' filter on 2005 Dec. 25, a bright core and irregular extension of the presumed host galaxy are clearly resolved in seeing of 1". The host magnitude listed above is measured in a 1.8" radius. Optical magnitudes were calibrated with Landolt standard stars, and positions were derived with respect to the USNO B1.0 catalog. The MDM images are posted at http://www.astro.columbia.edu/~jules/grb/050826/ Spectroscopy and deeper imaging are needed to measure the redshift and star-forming properties of the presumed host galaxy. This message may be cited."