[vsnet-grb-info 5058] GRB 070731: Swift/UVOT Upper Limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6765
SUBJECT: GRB 070731: Swift/UVOT Upper Limit
DATE:    07/08/27 13:21:53 GMT
FROM:    Frank Marshall at GSFC  <marshall at milkyway.gsfc.nasa.gov>

F.E. Marshall (NASA/GSFC) and A. Moretti (INAF-OAB)
report on behalf of the Swift team:

The Swift/UVOT observed the field of GRB 070731 starting 144 ks 
after the BAT trigger (Tueller et al., GCN Circ. 6691), which
occurred at 09:33:22 UT (Moretti et al., GCN Report 79.1). 
All of the UVOT exposures used the White (160-650 nm) filter, 
and the final exposure started 219 ks after the trigger. 
No XRT source was detected (Moretti et al., GCN Report 79.1) 
inside the BAT error circle, and we do not find any afterglow 
candidate inside the BAT error circle in the UVOT observations. 
The first long (1154 s) exposure that covered the entire 
BAT error circle started 155 ks after the BAT trigger. 
The 3-sigma upper limit for detecting a source is 20.9 mag. 
(uncorrected for the expected Galactic extinction corresponding 
to a reddening of E(B-V) = 0.04 mag in the direction of the burst 
(Schlegel et al. 1998)).