GCN Circular 29811

N. P. M. Kuin (UCL-MSSL) and Sbarrato (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210411C
66 s after the BAT trigger (Sbarrato et al., GCN Circ. 29794
Not found
 
 
).
A source consistent with the XRT position (Goad et al. GCN Circ. 29800
Not found
 
 
)
is detected in the initial UVOT exposures. Further detections were
reported by Strausbaugh et al. (GCN Circ 29802)

The preliminary UVOT position is:
    RA  (J2000) =  19:46:26.81 = 296.61170 (deg.)
    Dec (J2000) = -39:23:52.2  = -39.39784 (deg.)
with an estimated uncertainty of 0.43 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               66          216          147         17.16 +/- 0.03
v                  609          801           39         17.43 +/- 0.18
b                  535          555           20         17.82 +/- 0.17
u                  279          528          246         17.82 +/- 0.07
w1                 658         1280           78        >19.7
m2                 633         5836           83        >19.6
w2                 584         5600          255        >20.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.081 in the direction of the burst
(Schlegel et al. 1998).