TITLE:   GCN CIRCULAR
NUMBER:  20615
SUBJECT: GRB 170205A: Swift/UVOT Detection of a Fading Afterglow
DATE:    17/02/06 16:33:17 GMT
FROM:    Sam Emery at MSSL-UCL  <samuel.emery.15@ucl.ac.uk>

S.W.K. Emery (UCL-MSSL), E. Troja (NASA/GSFC/UMCP) and A.A. Breeveld (UCL-MSSL)  
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170205A
314 s after the BAT trigger (Troja et al., GCN Circ. 20603).
A source consistent with the XRT position
(Beardmore et al. GCN Circ. 20610) and also detected by
Guidorzi et al. GCN 20605, Butler et al. GCN 20609 and Kruehler et al. GCN 20612
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  17:28:40.69 = 262.16955 (deg.)
    Dec (J2000) = -00:03:47.3  =  -0.06313 (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(FC)       314             464           147        17.52 +/- 0.04
u(FC)                520             540             19        17.30 +/- 0.22
white             4361           4561          197         20.84 +/- 0.33
v                         619        17292        1101        >20.3
b                         545             565             19         17.79 +/- 0.24
u                      3951        12169          785         20.65 +/- 0.33
w1                     496        10592          924        >20.6
m2                  6287        17909          741        >20.6
w2                  4567        16378        1082        >21.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.35 in the direction of the burst
(Schlegel et al. 1998).