GCN Circular 22605

M. H. Siegel (PSU) and J. D. Gropp (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180404A
90 s after the BAT trigger (Gropp et al., GCN Circ. 22589
Not found
 
 
).
A source consistent with the XRT position
(Osborne et al. GCN Circ. 22592
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  05:34:11.64 =  83.54850 (deg.)
   Dec (J2000) = -37:10:03.9  = -37.16774 (deg.)
with an estimated uncertainty of 0.50 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)          90          240          147         19.47 +/- 0.09
white               90          770          180         19.34 +/ -0.10
white             45830       52026         1028        >21.66
v                  632         5179           99        >18.9
b                  558          750           39        >19.4
u (fc)              302         552          246         18.95 +/- 0.12
u                  303          726          265         18.95 +/ -0.14
w1                 682          701           19        >17.8
m2                 656          676           19        >17.4
w2                 607         5094          216         19.45 +/- 0.28

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).