TITLE:   GCN CIRCULAR
NUMBER:  30089
SUBJECT: GRB 210527A: Swift/UVOT Observations
DATE:    21/05/28 12:22:26 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>

M. H. Siegel (PSU) and S. L. Laha (GSFC/UMBC/CRESST)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210527A
3164 s after the BAT trigger (Laha et al., GCN Circ. 30081).
No optical afterglow consistent with the XRT position
(Evans et al., GCN Circ. 30083) 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          3164         3313          147         >20.2
white             3164         3932          344         >21.2
v                 4143         4343          197         >19.4
b                 3528         3727          197         >20.4
u                 3322         4895          331         >20.4
w1                4553         4753          197         >20.2
m2                4348         4548          197         >20.0
w2                3938         4138          197         >20.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.023 in the direction of the burst
(Schlegel et al. 1998).