GCN Circular 37487

M. H. Siegel (PSU) 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 240912A
115 s after the BAT trigger (Evans et al., GCN Circ. 37466
Not found
 
 
).
A fading source consistent with the XRT position (Goad et al.,
GCN Circ. 37470
Not found
 
 
) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  08:18:32.40 = 124.63499 (deg.)
   Dec (J2000) = +33:59:56.3  =  33.99897 (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 (fc)         117          265          144      17.44+/-0.05
white              608         1031          186      17.87+/-0.06
white             1185         1379           38      18.06+/-0.16
v                  657         1430           97      17.78+/-0.28
b                  583         5154          205      19.08+/-0.25
u (fc)             328          577          245      16.68+/-0.05
u                  731         5018          274      18.14+/-0.13
uvw1               707         1479           77      17.76+/-0.25
uvm2              1086         1106           19            >17.18
uvw2               633         1406           97      18.47+/-0.30

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.054 in the direction of the burst
(Schlegel et al. 1998).