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GCN Circular 4749

Subject
GRB 050826: Optical Afterglow and Host Galaxy
Date
2006-02-12T01:53:14Z (18 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
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."
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