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GCN Circular 8033

Subject
GRB 080727B: Swift/UVOT Upper Limits
Date
2008-07-27T18:25:27Z (16 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W.B. Landsman (NASA/GSFC/Adnet) and S. Immler (PSU) report on behalf of 
the Swift/UVOT team:

The Swift/UVOT observed the field of GRB 080727B starting 105s after the 
BAT trigger (Immler et al., GCN Circ. 8022).   We do not find any 
source, in any of the UVOT observations, at either the UVOT-enhanced XRT 
position of the afterglow (Goad et al. GCN Circ. 8026) or the proposed 
KAIT afterglow position (Li et al., GCN 8024).     The 3-sigma upper 
limits for detecting a source at this location in single exposures are:

Filter       T_start      Exp(s)    Mag (3-sigma upper limit)
----------------------------------------------------------
   v          211        393     >20.6
  uvw1        642         15     >17.9
  uvm2        617         19     >17.6
  white       105         98     >21.0
----------------------------------------------------------


The quoted upper limits have not been corrected for the expected 
Galactic extinction along the line of sight corresponding to a large 
reddening of E_{B-V} = 1.9 mag.  All photometry is on the UVOT flight 
system described in Poole et al. (2008, MNRAS, 383, 627).

Combining the UVOT upper limits with the KAIT detection at R~18.3 (Li et 
al., GCN 8024) suggest that there is either high extinction, very fast 
decline in brightness (the UVOT observations began 57 seconds after the 
KAIT observations ), or high redshift.      The UVOT results are 
obtained at shorter wavelengths, and for example, the UVOT v filter is 
expected to suffer an additional ~1.4 mag of extinction, assuming that  
E(B-V) = 1.9 and that the KAIT clear filter corresponds roughly to the R 
band.    The results may also be consistent with a high redshift burst 
(5.5 < z <6.5) which is only observable at wavelengths longward of ~6000 A.
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