GCN Circular 16710

F. E. Marshall (NASA/GSFC) and B. Sbarufatti (INAF-OAB/PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 140817A
101 s after the BAT trigger (Sbarufatti et al., GCN Circ. 16695
Not found
 
 
).
A fading source consistent with the UVOT-enhanced XRT position
(Osborne et al. GCN Circ. 16697
Not found
 
 
) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
  RA  (J2000) =  08:29:03.21 = 127.26336 (deg.)
  Dec (J2000) =  58:11:24.7  =  58.19020 (deg.)
with an estimated uncertainty of 0.53 arc sec. (radius, 90% confidence).

Preliminary detection and 3-sigma upper limits 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              101         1017          334         20.3 +/- 0.17
white             5426        18414         1794        >21.6
v                  642         1068           58        >18.0
b                  568          762           39        >18.5
u                  313         4899          435        >20.5
w1                 692         1117           39        >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.15 in the direction of the burst
(Schlegel et al. 1998).