TITLE:   GCN CIRCULAR
NUMBER:  9898
SUBJECT: GRB 090904B: Swift/UVOT Refined Analysis
DATE:    09/09/05 05:45:47 GMT
FROM:    Tyler Pritchard at PSU  <tapritchard@astro.psu.edu>

T. A. Pritchard (PSU) and D'Elia (ASDC) report on behalf of the
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090904B,
138 seconds
after the BAT trigger (D'Elia et al., GCN Circ. 9881). We do not detect
any source
at the UVOT-enhanced XRT position (J.P. Osbourne et al., GCN Circ.9887).

The 3-sigma upper limits for the exposures are:

Filter   T_start(s)   T_stop(s)   Exp(s)  Mag (3-sigma upper limit)
-------------------------------------------------------------
white      138          1357       369      > 22.17
v          625          1237        78      > 19.08
b          551           1335        78      > 20.08
u          295            545       246      > 20.41
-------------------------------------------------------------

The quoted upper limits have not been corrected for the highly uncertain
extinction
corresponding to a reddening along the line of sight of of E_(B-V) =
1.76 mag
Schlegel et al., (1998, ApJS, 500, 525).  All photometry is on the UVOT
photometric
system described in Poole et al. (2008, MNRAS, 383, 627).