TITLE:   GCN CIRCULAR
NUMBER:  13539
SUBJECT: GRB 120729A: Swift/UVOT Detection
DATE:    12/07/29 18:39:35 GMT
FROM:    Samantha Oates at MSSL  <sro@mssl.ucl.ac.uk>

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).
A source consistent with the XRT position (Beardmore et al., GCN Circ. 13534)
and the optical position reported by FTN (Virgili et al., GCN Circ. 13531) 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).