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GCN Circular 4749

GRB 050826: Optical Afterglow and Host Galaxy
2006-02-12T01:53:14Z (18 years ago)
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

Spectroscopy and deeper imaging are needed to measure the redshift 
and star-forming properties of the presumed host galaxy.

This message may be cited."
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