TITLE:   GCN CIRCULAR
NUMBER:  23062
SUBJECT: GRB 180727A: Swift/UVOT Upper Limits
DATE:    18/07/30 18:03:24 GMT
FROM:    Frank Marshall at Swift/UVOT  <marshall@milkyway.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and A. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180727A
77 s after the BAT trigger (Beardmore et al., GCN Circ. 23043).
No optical afterglow consistent with the enhanced XRT position
(D'Elia et al., GCN Circ. 23045)
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) exposures and subsequent exposures are:

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

white_FC            77          227          147         >20.9
u_FC               290          303           12         >18.4
white             4280         5915          393         >21.7
v                 4690         6312          379         >19.6
b                 4075         5710          393         >21.2
u                 5305         5505          197         >20.3
uvw1              5101         5301          197         >20.0
uvm2              4895         5095          197         >21.0
uvw2              4485         6122          393         >21.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).