GCN Circular 3954

M. De Pasquale (MSSL), M. Goad (U. Leicester),
F. Marshall (GSFC), J. Norris(GSFC), K. Hurley
(Berkeley), N. Gehrels, on behalf of the Swift/UVOT team

The Swift/UVOT began observing the field of
GRB050908 at 05:44:15 UT, 104 seconds after the
BAT trigger (Goad et al., GCN 3942
Not found
 
 
). No new
source with respect to the DSS was detected in
the initial 100 s V-band UVOT image with a
significance of 3 sigma at the position of the
optical afterglow found by Torii et al.
(GCN 3943
Not found
 
 
). The corresponding 3 sigma upper
limit is 18.8.

  There was also no optical/UV counterpart detected
in the summed images from all filters, down to the
following 3 sigma magnitude upper limits:

  Filter  T_range(s)  Exp (s)  3sig UL

    V      104-6922    942      19.9
    B      250-5254    1020     21.1
    U      236-1098    190      19.5
    UVW1   223-993     100      19.1
    UVM2   208-11040   987      20.9
    UVW2   265-6163    997      20.6

Where T_range is the time post-trigger over which
the summed images were accumulated and Exp is the
total exposure time. The magnitudes upper limits
are not corrected for extinction.

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