TITLE:   GCN CIRCULAR
NUMBER:  32085
SUBJECT: GRB 220521A: Swift/UVOT Upper Limits
DATE:    22/05/22 13:57:22 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and S. Dichiara (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 220521A
100 s after the BAT trigger (Dichiara et al., GCN Circ. 32076).No optical
afterglow consistent with the XRT position (Evans et al. GCN Circ. 32081)
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           100          250          147         >20.8
u_FC               312          548          232         >19.2
white              100         4178          344         >21.5
v                 4389         4589          197         >19.5
b                 3773         3973          197         >20.4
u                  312         5050          278         >19.4
w1                4798         4998          197         >20.2
m2                4593         4793          197         >19.7
w2                4184         4383          197         >19.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.185 in the direction of the burst
(Schlegel et al. 1998).