TITLE:   GCN CIRCULAR
NUMBER:  26962
SUBJECT: GRB 200131A: Swift/UVOT Detection
DATE:    20/02/01 14:37:48 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and B. Sbarufatti (PSU)report on behalf of
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200131A
78 s after the BAT trigger (Sbarufatti et al., GCN Circ. 26953).
A source consistent with the XRT position (Goad et al. GCN Circ. 26956)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  00:12:22.57 =   3.09405 (deg.)
    Dec (J2000) = +51:07:00.3  =  51.11675 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

The source has been detected also by MASTER (Lipunov et al. GCN Circ. No.
26954), RATIR (Butler et al., GCN Circ. No. 26957), MacDonalds Observatory
(Strausbaugh et al., GCN Circ. No. 26959),  and VIRT (Gokuldass et al.,
GCN Circ. No. 26960.

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               78          227          147         15.47 +/- 0.02
v                 4281         5919          393         19.57 +/- 0.28
b                 5103         5303          197         19.53 +/- 0.16
u                  290          323           32         16.09 +/- 0.08
w1                4692         4892          197         18.48 +/- 0.18
m2                4486         6124          393         18.98 +/- 0.20
w2                4076         5714          393         19.06 +/- 0.19

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.17 in the direction of the burst
(Schlegel et al. 1998).