TITLE:   GCN CIRCULAR
NUMBER:  12286
SUBJECT: GRB 110818A: Swift/UVOT Upper Limits
DATE:    11/08/19 19:29:06 GMT
FROM:    Tyler Pritchard at PSU  <tapritchard@astro.psu.edu>

T. A. Pritchard (PSU) and C. B. Markwardt (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110818A
379 s after the BAT trigger (Markwardt et al., GCN Circ. 12279).
No optical afterglow consistent with the Enhanced Swift-XRT position
(GCN Circ. 12285) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are:

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

v                  379        14423         1513         >20.8
b                  477        18642         2455         >22.2
u                  452         8009          813         >20.4
w1                 428         7804          646         >20.9
m2                7399         7599          197         >20.9
w2                6989        13752         1082         >21.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).