TITLE:   GCN CIRCULAR
NUMBER:  41291
SUBJECT: GRB 250807A: Swift/UVOT Detection
DATE:    25/08/08 16:24:35 GMT
FROM:    s.shilling@lancaster.ac.uk

S. P. R. Shilling (Lancaster U.) and N. J. Klingler (GSFC/UMBC/CRESSTII)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250807A
111 s after the BAT trigger (Klingler et al., GCN Circ. 41262).
A source consistent with the enhanced XRT position
(Evans et al., GCN Circ. 41270) is detected in the initial UVOT exposures.

Preliminary detections 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              111          261          147         18.00 +/- 0.04
v                  653         1769          136        >18.8
b                  579         1695          117        >19.5
u                  323         1840          361         19.88 +/- 0.31
w1                 702         1818          117        >19.0
w2                 801          821           19        >17.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.011 in the direction of the burst
(Schlegel et al. 1998).