TITLE:   GCN CIRCULAR
NUMBER:  33292
SUBJECT: GRB 230204B: Swift/UVOT Upper Limits
DATE:    23/02/06 20:50:39 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>

M. H. Siegel (PSU) and V. D’Elia (SSDC & INAF-OAR)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230204B
80 ks after the MAXI trigger (Serino et al., GCN Circ. 33265).
No optical afterglow consistent with the optical or XRT positions
(Swain et al., GCN Circ. 33269, Smartt et al., GCN Circ. 33278, D’Elia et al.,
GCN Circ. 33285) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:

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

v                81062       109630          314         >19.1
b                80652       109220          314         >20.1
u                80567       109136          314         >19.8
w1               80403       109052          629         >20.1
m2               81146       109877         2154         >20.9
w2               80737       109546         1259         >20.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.109 in the direction of the burst
(Schlegel et al. 1998).