GCN Circular 21454

GRB 170810A: Swift/UVOT Detection

S. J. LaPorte (PSU) and S. L. Gibson (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170810A
85 s after the BAT trigger (Gibson et al., GCN Circ. 21450).
A source consistent with the XRT position
(Goad et al. GCN Circ. 21451)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  12:31:45.33 = 187.93889 (deg.)
    Dec (J2000) = +03:39:38.9  =   3.66081 (deg.)
with an estimated uncertainty of 0.42 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               85          235          147         14.64 +/- 0.02
v                  628          648           20         15.88 +/- 0.13
b                  554          574           20         16.62 +/- 0.10
u                  299         1493          281        >19.3
w1                 677         1473           97        >18.9
w2                 604          623           19        >18.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).