TITLE:   GCN CIRCULAR
NUMBER:  35135
SUBJECT: 231118A: Swift-UVOT Detection
DATE:    23/11/20 12:42:03 GMT
FROM:    Paul Kuin at MSSL <npkuin@gmail.com>

N.P.M. Kuin (MSSL/UCL) and S. L. Laha (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 231118A
105 s after the BAT trigger (Laha et al., GCN Circ. 35101).
A source consistent with the XRT position (Evans et al., GCN Circ. 35106)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  00:19:19.26 =   4.83024 (deg.)
    Dec (J2000) = -48:02:24.1  = -48.04004 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

Preliminary detections 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              105          255          147         17.28 +/- 0.03
v                 1052         1071           20         16.59 +/- 0.16
b                  573          593           19         17.10 +/- 0.11
u                  318          568          246         16.69 +/- 0.04
w1                1618         1638           19         17.18 +/- 0.24

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.013 in the direction of the burst
(Schlegel et al. 1998).