TITLE:   GCN CIRCULAR
NUMBER:  32875
SUBJECT: GRB 221027B: Swift/UVOT Upper Limits
DATE:    22/10/28 15:11:15 GMT
FROM:    Alexander Belles at PSU/Swift  <aub1461@psu.edu>

A. Belles (PSU) and A. Y. Lien (U. Tampa)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 221027B
131 s after the BAT trigger (Lien et al., GCN Circ. 32867).
No optical afterglow consistent with the XRT position
(Beardmore et al. GCN Circ. 32868)
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           131          281          147         >21.1
u_FC               344          594          246         >20.2
white              131         1544          392         >21.5
v                  673         1594          117         >19.2
b                  599         1520           97         >19.4
u                  344         1661          335         >20.4
w1                 722         1644           97         >18.8
m2                 698          718           19         >17.6
w2                 111          841           30         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.033 in the direction of the burst
(Schlegel et al. 1998).