TITLE:   GCN CIRCULAR
NUMBER:  23120
SUBJECT: GRB 180809B: Swift/UVOT Detection
DATE:    18/08/10 16:29:24 GMT
FROM:    Sam LaPorte at PSU  <sjl5346@psu.edu>

GRB 180809B: Swift/UVOT Detection

S. Sebzda (PSU) and M. Moss (George Washington University)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180809B
82 s after the BAT trigger (Moss et al., GCN Circ. 23105).
A fading source consistent with the XRT position
(Moss et al. GCN Circ. 23105)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  19:58:47.96 = 299.69984 (deg.)
    Dec (J2000) = -15:17:57.1  = -15.29920 (deg.)
with an estimated uncertainty of 0.48 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               81          231          293         18.99+-0.07
white              573         6926          441        >21.55
v                  623         7289          444        >19.8
b                  549         6721          294        >20.9
u                  294         6516          520        >21.0
w1                 672        13027          915        >20.7
m2                 648        11053          906        >20.9
w2                 599        16967         1262        >21.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.16 in the direction of the burst
(Schlegel et al. 1998).