TITLE:   GCN CIRCULAR
NUMBER:  40471
SUBJECT: GRB 250516A: Swift/UVOT Detection
DATE:    25/05/16 22:17:55 GMT
FROM:    Sam Shilling at Lancaster University <shilling.sam@gmail.com>

S. P. R. Shilling (Lancaster U.) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250516A
108 s after the BAT trigger (Beardmore et al., GCN Circ. 40467). A source
consistent with the enhanced XRT position (Evans et al., GCN Circ. 40468)
is detected in the initial UVOT exposures.

The preliminary detection and 3-sigma upper limits using the UVOT photometric
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are: 

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

white              108         1715          411         20.5 +/- 0.3
v                  650         1765          136        >18.5
b                  576         1691          117        >19.2
u                  320         1838          362        >19.7
w1                 699         1814          117        >18.8
w2                 626         1741           97        >19.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.062 in the direction of the burst
(Schlegel et al. 1998).