TITLE:   GCN CIRCULAR
NUMBER:  31317
SUBJECT: GRB 211221A: Swift/UVOT Upper Limits
DATE:    21/12/28 00:14:08 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>

M. H. Siegel (PSU) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 211221A
63 s after the BAT trigger (Page et al., GCN Circ. 31273).
No optical afterglow consistent with the XRT position (Evans et al.
GCN Circ. 31275) 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            63          213          147         >20.7
u_FC               275          525          246         >20.1
white               63         1010          317         >21.1
v                  606          799           39         >18.6
b                  531          724           39         >19.4
u                  275          872          285         >20.0
w1                 655          848           39         >18.1
m2                 631          650           19         >17.8
w2                 582          774           39         >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.143 in the direction of the burst
(Schlegel et al. 1998).