TITLE:   GCN CIRCULAR
NUMBER:  39948
SUBJECT: GRB 250330A: Swift/UVOT Upper Limits
DATE:    25/03/30 17:15:45 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

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

The Swift/UVOT began settled observations of the field of GRB 250330A
3944 s after the BAT trigger (Cenko et al., GCN Circ. 39938).
No optical afterglow consistent with the XRT position (Osborne et al., GCN
Circ. 39947) 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 first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC          3944         4094          147         >21.2
white             3944         4094          147         >21.2
v                 4101         4300          197         >20.0
b                 4921         5109          185         >20.9
u                 4716         4915          197         >20.0
w1                4511         4711          197         >21.3
m2                4306         4505          197         >19.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.147 in the direction of the burst
(Schlegel et al. 1998).