TITLE:   GCN CIRCULAR
NUMBER:  27709
SUBJECT: GRB 200509A: Swift/UVOT Detection
DATE:    20/05/10 00:34:40 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and E. Troja (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200509A
123 s after the BAT trigger (Troja et al., GCN Circ. 27701). A source
consistent with the XRT position  (Troja et al. GCN Circ. 27701)  is
detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  07:45:41.28 = 116.42200 (deg.)
    Dec (J2000) = -04:37:49.3  =  -4.63035 (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              123          273          147         18.92 +/- 0.08
v                  611         1738          122        >18.6
b                  537         1678          117        >19.8
u                  281          531          246         18.46 +/- 0.10
w1                 660         1628          117        >19.0
m2                 636         1604          117        >19.0
w2                 587         1728          136        >19.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.13 in the direction of the burst
(Schlegel et al. 1998).