GCN Circular 4038

S. Rosen (MSSL), S. T. Holland (GSFC/USRA),  F. Marshall(GSFC), 
P. Boyd (GSFC-UMBC), N. Gehrels (GSFC) on behalf of the Swift/UVOT team.


The Swift/UVOT began observing the field of the short-soft burst, GRB050925, 
at 09:06:03 UT, 90s seconds after the BAT trigger (Holland et al., GCN 4034
Not found
 
 
). 
There has been no reported XRT detection of a fading afterglow and no 
counterpart found in ground-based observations (GCN 4035
Not found
 
 
 and 4036
Not found
 
 
) so 
no positional information other than the BAT location (revised position 
from Markwardt et al., GCN 4037
Not found
 
 
) is currently available.

Within the 1.5 arcmin BAT error circle (GCN 4037
Not found
 
 
), no new optical/UV source 
is detected and we derive the following 3 sigma upper limit magnitudes 
on any optical/UV counterpart in the summed images in each UVOT filter 
(from 6" radius apertures centred on the BAT location which is 
representative of the local background).

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

      V        90-50567     3885     20.2
      B      3787-57196     4600     21.8
      U      3682-56297     4654     21.2
      UVW1   3578-52239     4080     21.4
      UVM2   3473-51474     4541     21.8
      UVW2   3892-62080     4356     21.8

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 which is high since 
the BAT position is in the galactic plane.