TITLE:   GCN CIRCULAR
NUMBER:  33266
SUBJECT: GRB 230204A: Swift/UVOT Upper Limits
DATE:    23/02/04 23:36:26 GMT
FROM:    Sam LaPorte at PSU  <sjl5346@psu.edu>

 S. J. LaPorte (PSU) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230204A
156 s after the BAT trigger (D'Ai et al., GCN Circ. 33260).
No optical afterglow consistent with the XRT position
(Evans et al. GCN Circ. 33261)
is detected in the initial UVOT exposures.
A known source with no significant signs of fading
is detected 2.88 arcsec from the XRT position at:

RA (J2000): 15h 52m 47.83s
Dec (J2000): -50d 54' 56.74"

Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           156            306          147          >17.5
u_FC                  314            564          246         >19.1
white                  156          1372          373         >17.8
v                         645          1596          117         >15.9
b                         570          1521            97         >17.9
u                         314          5553          382         >19.1
w1                      695           5489          274         >19.1
m2                      670          1446            97         >18.8
w2                       621          1571          117         >18.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 2.516 in the direction of the burst
(Schlegel et al. 1998).