GCN Circular 7016
Subject
Swift UVOT upper limits to GRB071028
Event
Date
2007-10-29T17:12:39Z (18 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL/UCL) and J.L. Racusin (PSU) report on behalf of the Swift
UVOT team:
The Swift/UVOT observed the field of GRB 071028 (GCN 7012; Racusin et al.)
beginning 128 seconds after the BAT trigger. No afterglow is detected in
any of the UVOT filters within the XRT error circle (Racusin et al., GCN
7014). As already noted by Xin et al. (GCN 7015), the refined XRT position
(Racusin et al., GCN 7014) lies next to a very bright star (V<10 mag),
severely limiting the detection of an optical afterglow.
In the case of the white band and optical filters (v,b,u), contamination
from the nearby, bright star is causing the exposures to be affected by
coincidence loss to a degree that is outside the photometrically
calibrated range of UVOT. This limits the depth of our observations at the
XRT position in these filters to white > 13.86, v > 11.46, b > 12.68 and u
> 11.91.
The 3-sigma upper limits at the XRT position in co-added UV exposures are as
follows:
Filter Tmid Exp Magnitude
(s) (s) (3-sigma UL)
uvw1 5044 412 > 19.89
uvm2 4847 413 > 20.32
uvw2 5014 213 > 19.67
where Tmid is the mid time of the observations. The values quoted above are not
corrected for the expected Galactic extinction corresponding to a reddening of
E_{B-V} = 0.06 mag in the direction of the burst (Schlegel et al. 1998).