TITLE:   GCN CIRCULAR
NUMBER:  13932
SUBJECT: GRB 121027A: Swift/UVOT Possible Detection
DATE:    12/10/30 17:59:26 GMT
FROM:    Frank Marshall at GSFC  <femarsha@khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 121027A
77 s after the BAT trigger (Evans et al., GCN Circ. 13906).
A source consistent with the XRT position (Beardmore et al. GCN Circ. 13916)
and the nIR position (Starling et al. GCN Circ. 13911)
is weakly detected in the initial UVOT exposures.

The 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               77         1192          353         21.55 +/- 0.25
v                  619         1239           75        >19.5
b                  544         1167           58        >19.7
u                  289         1143          285        >20.6
w1                 668         1118           58        >19.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).