GCN Circular 13539

S. R. Oates (MSSL-UCL) and T. N. Ukwatta (MSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120729A
77 s after the BAT trigger (Ukwatta et al., GCN Circ. 13530
Not found
 
 
).
A source consistent with the XRT position (Beardmore et al., GCN Circ. 13534
Not found
 
 
)
and the optical position reported by FTN (Virgili et al., GCN Circ. 13531
Not found
 
 
) is 
detected in the initial UVOT exposures.

The preliminary UVOT position is:
  RA  (J2000) =  00:52:17.83 =  13.07431 (deg.)
  Dec (J2000) = +49:56:23.1  =  49.93974 (deg.)
with an estimated uncertainty of 0.50 arc sec. (radius, 90% confidence).

Preliminary detections 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               77          227          147         15.33 +/- 0.02
v                  620          640           20         15.92 +/- 0.15
b                  545          564           20         16.56 +/- 0.12
u                  289          539          246         15.78 +/- 0.04
w1                4113         4313          197         18.49 +/- 0.16
m2                3908         4108          197         18.91 +/- 0.25
w2                 595          615           20         17.57 +/- 0.32

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.16 in the direction of the burst
(Schlegel et al. 1998).