GCN Circular 21411

S.W.K. Emery (UCL-MSSL) and S. J. LaPorte (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170803A
88 s after the BAT trigger (LaPorte et al., GCN Circ. 21405
Not found
 
 
).
GRB 170803A was also triggered by Fermi GBM
(Veres and Meegan GCN Circ. 21406
Not found
 
 
)
A fading source consistent with the XRT position
(Beardmore et al., GCN Circ. 21407
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  11:39:44.11 = 174.93380 (deg.)
    Dec (J2000) = -16:18:38.0  = -16.31055 (deg.)
with an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence).

Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white_FC            88          238          147         18.10 +/- 0.06
white              580         2241          322         19.69 +/- 0.12
u_FC               300          550          246         18.58 +/- 0.16
u                  775         2366          175         >19.34
b                  556         2386          191         20.02 +/- 0.35
uvw1              6216        23821          982         >20.74
uvm2             17025        17715          679         >20.57
uvw2              5602        30135          990         >21.05

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).