TITLE:   GCN CIRCULAR
NUMBER:  35705
SUBJECT: GRB240204A: Swift/UVOT Upper Limits
DATE:    24/02/08 15:37:24 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

M. H. Siegel (PSU) and and S. B Cenko (GSFC) report on behalf of the
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240204A 
4.8 ks after the BAT trigger (Cenko et al., GCN Circ 35666). No optical
afterglow consistent with either the optical (Pozanenko et al., GCN
Circ. 35670) or X-ray (Beardmore et al., GCN Circ. 35671) position 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 of
the candidate afterglow field are:

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

white             5887         6087          196            >20.70
v                 4862         6498          393            >19.32
b                 5683         5882          196            >19.98
u                 5477        28539         1048            >20.54
uvw1              5272         5472          196            >19.26
uvm2              5067         6669          360            >19.36
uvw2              6093         6293          196            >19.42

The magnitudes in the table are not corrected for the Galactic extinction
due to the high but uncertain reddening in the direction of the burst
(Schlegel et al. 1998).