GCN Circular 8559

S. T. Holland (CRESST/GSFC/USRA) and R. Margutti (Univ Bicocca & OAB)
report on the behalf of the Swift UVOT team:

       The Swift/UVOT observed the field of GRB 081126 starting 56 s
after the BAT trigger (Margutti, et al. 2008, GCN Circ. 8554
Not found
 
 
).
Settled exposures started at T+75 s.  We do not find any new source,
relative to the DSS or 2MASS, or any variable source inside the
UVOT-enhanced XRT error circle (Osborne, et al. 2008, GCN Circ. 8556
Not found
 
 
).
Preliminary 3-sigma upper limits for detecting a source in the
co-added images, using a 2.5 arcsecond radius circular aperture, are

Filter   T_start   T_stop   Exp(s)     Mag
------------------------------------------
  white        75      225     147    >21.3
     u        289      420     129    >20.1

     v       5161     5361     197    >19.7
     b       4546     6183     393    >20.9
     u       3133     5976     326    >20.7
   uvw1      5572     5771     197    >20.0
   uvm2      5366     5566     197    >19.8
   uvw2      4957     6398     199    >20.0
  white      4751     6388     393    >21.8
------------------------------------------

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.78 mag (Schlegel, et al., 1998, ApJS, 500,
525).  All photometry is on the UVOT flight system described in Poole
et al. (2008, MNRAS, 383, 627).

      The 2MASS point source 21340333+4842361 is located 3.2 arcsec
north of the centre of the XRT error circle.  Our photometry is
slightly contaminated by an uncatalogued source approximately 2.6
arcsec northwest of the centre of the XRT error circle.  This source
appears to be extended and may be the host galaxy of GRB 081126.
Preliminary magnitudes are

Filter     Mag  Err
----------------------------------------
     v    19.2   0.3
     b    20.2   0.2
     u   >20.9        3-sigma upper limit
   uvw1  >20.1        3-sigma upper limit
   uvm2  >19.9        3-sigma upper limit
   uvw2  >20.1        3-sigma upper limit
  white   20.2   0.2
----------------------------------------

The detection in the b filter, combined with the lack of a detections
in the u and UV filters, is consistent with this source having a
redshift of approximately 2.8 < z < 4.5.  This corresponds to a
physical separation of approximately 18 proper kpc assuming a
cosmology with (H_0,Omega_matter,Omega_Lambda) = (70,0.3,0.7).