GCN Circular 17085

F. E. Marshall (NASA/GSFC) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 141121A
371 s after the BAT trigger (Lien et al., GCN Circ. 17075
Not found
 
 
).
A source consistent with the optical position
(Tanga et al. GCN Circ. 17078
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  08:10:40.63 = 122.66928 (deg.)
   Dec (J2000) =  22:13:02.2  =  22.21728 (deg.)
with an estimated uncertainty of 0.5 arcsec. (radius, 90% confidence).

The source shows an unusual light curve with little evidence for variability.
The source is detected in all UVOT filters although the detections in v and w2
are not highly significant. 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              371          520          147        >20.1
white             6067         6266          197         20.2 +/- 0.2
v                  527          547           19        >18.3
v                15373        16025          635         20.3 +/- 0.3
b                 5862         6062          197         19.8 +/- 0.2
u                 5562         5714          149         19.4 +/- 0.2
u                27756        28325          556         19.3 +/- 0.1
w1                3830         3897           66         19.4 +/- 0.3
w1               26850        27750          886         19.7 +/- 0.1
m2               21039        21939          886         20.4 +/- 0.2
w2                9514        12083          771         21.2 +/- 0.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).