GCN Circular 23274

S.W.K. Emery (UCL-MSSL) and J. D. Gropp (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180925A
119 s after the BAT trigger (Gropp et al., GCN Circ. 23268
Not found
 
 
).
A fading source consistent with the XRT position
(Goad et al. GCN Circ. 23271
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  21:00:48.70 = 315.20292 (deg.)
    Dec (J2000) = -64:27:24.82 = -64.456894 (deg.)
with an estimated uncertainty of 0.22 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              119          269          147         19.73 +/- 0.17
white              557         6943          674         20.32 +/- 0.13
v                  607         7354          549         >19.66
b                  533         6739          347         20.89 +/- 0.37
u                  277         6533          579         19.78 +/- 0.21
uvw1               657         7755          540          20.07 +/- 0.29
uvm2              1062         7559          413         >20.14
uvw2               583         7149          510         >20.60

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).