TITLE:   GCN CIRCULAR
NUMBER:  20587
SUBJECT: GRB 170202A: Swift/UVOT Detection
DATE:    17/02/03 05:18:40 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170202A
84 s after the BAT trigger (Racusin et al., GCN Circ. 20575). A source
consistent with the enhanced XRT position (Osborne et al., GCN 20586)
and is detected in the initial UVOT exposures. No detection in the U and
UV filters is consistent with the reported redshift (de Ugarte Postigo et
al,
GCN Circ. 20584).

The preliminary UVOT position is:
    RA  (J2000) =  10:10:03.49 = 152.51454 (deg.)
    Dec (J2000) = +05:00:41.8  =   5.01161 (deg.)
with an estimated uncertainty of 0.44 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               84          233          147         18.31 +/- 0.05
v                  625         1419           97         18.27 +/- 0.20
b                  551         1345           78         19.18 +/- 0.19
u                  295         1837          363        >21.1
w1                 675         1812          136        >19.6
w2                1030         1050           19        >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).