GCN Circular 17933

S. R. Oates (IAA-CSIC/UCL-MSSL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of V404 Cyg
184 s after the BAT trigger (Barthelmy et al., GCN Circ. 17929
Not found
 
 
).
A source consistent with the XRT position is detected in the initial
UVOT exposures. The white filter is approximately constant for
the first 600s after the trigger, but a slight increase in flux is observed
in white after this time until observations cease at ~900s. The increase
in flux is also observed in the v and b filters.

Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag
white (FC)         184          334          147         15.72 +/- 0.02
white              875          919           44         15.34 +/- 0.03
v                  673          693           19         14.58 +/- 0.07
v                  848          867           19         14.22 +/- 0.06
b                  599          619           19         16.17 +/- 0.08
b                  773          793           19         15.78 +/- 0.07
u (FC)             342          591         246         16.13 +/- 0.04
u                  748          768           20         16.06 +/- 0.11
w1                 722          742           19         > 17.66
m2                 698          717           19         > 17.45
w2                 649          843           39         > 18.37

The magnitudes in the table are not corrected for the large Galactic
extinction due to the reddening of E(B-V) = 2.02 in the direction of the burst
(Schlegel et al. 1998).