GCN Circular 30832

N. P. M. Kuin (UCL-MSSL) and E. Troja (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210912A
60 s after the BAT trigger (Troja et al., GCN Circ. 30820
Not found
 
 
).
A source consistent with the optical position
(Hu et al. GCN Circ. 30823
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  08:39:34.27 = 129.89280 (deg.)
    Dec (J2000) = +79:13:17.1  =  79.22141 (deg.)
with an estimated uncertainty of 0.47 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               60          209          147         18.73 +/- 0.08
v                  602          621           19        >17.8
b                  528          547           19        >18.3
u                  272          490          214         19.56 +/- 0.31
w2                 577          597           19        >18.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.027 in the direction of the burst
(Schlegel et al. 1998).