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.