TITLE:   GCN CIRCULAR
NUMBER:  43105
SUBJECT: GRB 251214B: Swift/UVOT Detection
DATE:    25/12/15 05:01:50 GMT
FROM:    Paul Kuin at MSSL <npkuin@gmail.com>

N.P.M. Kuin (MSSL/UCL) and R. Eyles-Ferris (U. Leicester) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251214B  64 s
after the BAT trigger (Eyles-Ferris et al., GCN Circ. 43089).  A source
consistent with the XRT position Evans et al.  GCN Circ. 43098) is detected
in the initial UVOT exposures.

There were early reports of the optical afterglow from Zhe Kang et al. (GCN
Circ. 43093) and S.Y. Fu et al. (GCN Circ. 43097).

The preliminary UVOT position is:
    RA  (J2000) =  22:00:50.53 = 330.21053 (deg.)
    Dec (J2000) = -09:09:46.4  =  -9.16290 (deg.)
with an estimated uncertainty of 0.43 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               64          214          147         17.21 +/- 0.03
v                  606          800           39         17.09 +/- 0.17
b                  532          724           39         18.08 +/- 0.17
u                  277          527          246         17.76 +/- 0.08
w1                 655         1472           97        >18.9
m2                 630         1447           97        >20.3
w2                 582         5213          136        >19.6

The magnitudes in the table are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.039 in the direction of the burst  (Schlegel
et al. 1998).