TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3901
SUBJECT: GRB050827: Swift/UVOT upper limits
DATE:    05/08/29 02:25:11 GMT
FROM:    Alexander Blustin at MSSL-UCL  <ajb@mssl.ucl.ac.uk>

A. J. Blustin (UCL-MSSL), M. Capalbi (ASDC), F. Marshall (GSFC),
J. Nousek (PSU), N. Gehrels (GSFC) on behalf of the Swift UVOT team

Swift/UVOT began observing the field of GRB050827 17.8 hours after
the BAT trigger (Capalbi, et al., GCN 3893); previous to that, the
target was unobservable due to a moon constraint. No new source with 
respect to the DSS image is detected in the XRT error circle
(Capalbi, et al., GCN 3899) down to the following upper limits in
the six filters:

Filter  T-range (hrs)  Exp (s)  3sig_limit

V        20.9-24.3     1800     20.1
B        19.5-26.2     2444     21.0
U        19.3-25.9     2699     21.1
UVW1     18.1-25.7     2939     20.6
UVM2     17.8-24.6     2531     20.7
UVW2     20.6-24.1     1800     20.8

Where T_range is the time range in hours post-trigger over which the
summed images were accumulated and Exp is the total exposure time
(in seconds) of the summed image. The magnitude upper limits are not
corrected for extinction.

These magnitudes are based on preliminary zero-points, measured
in orbit, and will require refinement with further calibration.