TITLE:   GCN CIRCULAR
NUMBER:  42786
SUBJECT: GRB 251118A: Swift/UVOT Detection
DATE:    25/11/20 22:23:37 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251118A 31.3 ks after the Fermi trigger (GCN Circ. 42743). A fading source consistent with the XRT position (Osbourne et al., GCN Circ. 42782) is detected in the UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  10:14:01.01 = 160.00422 (deg.)
    Dec (J2000) = -34:31:21.1  = -34.52254 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

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            31521        52651          885      18.79+/-0.05
white           108251       159027         1113      20.11+/-0.10
v                31678        42929          845      18.60+/-0.19
v               108564       147691          662            >19.73
u                31363        52627         2489      18.41+/-0.05
u               107942       158555         1113      19.61+/-0.15

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.057 in the direction of the burst
(Schlegel et al. 1998).