GCN Circular 13973

S. R. Oates (MSSL-UCL) and J. R. Cummings (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 121117A
s after the BAT trigger (Cummings et al., GCN Circ. 13967
Not found
 
 
).
We find an optical afterglow consistent with the XRT position
(Beardmore et al. GCN Circ. 13972
Not found
 
 
) in the initial UVOT white exposure.
The refined UVOT position is (RA,DEC) = 31.61063, 7.41956 (J2000), 
which is equivalent to:

RA (J2000)  =  02:06:26.56
Dec (J2000) =  +07:25:10.5

with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence).

Preliminary magnitudes and 3-sigma upper limits using the UVOT photometric 
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial 
exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white (FC)        57            205          146         19.17 +/- 0.10
white             4606        10267         1150         >21.9
v                 3580        11882         1077         >20.3
b                 4400         6037          393         >20.6
u                 4195         5831          393         >20.3
w1                3990         5627          393         >20.3
m2                3785         5421          393         >20.2
w2                4811        11174         1082         >21.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).