TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3394
SUBJECT: GRB050509a: Swift UVOT observations
DATE:    05/05/09 16:04:32 GMT
FROM:    Katie McGowan at MSSL-UCL  <km2@mssl.ucl.ac.uk>

T. Poole (MSSL), C. Hurkett (Leicester), S. Hunsberger (PSU), A. Breeveld
(MSSL), P. Boyd (GSFC), N. Gehrels (GSFC), K. Mason (MSSL), J. Nousek
(PSU), on behalf of the Swift UVOT team

The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of
GRB050509a on May 09, 2005 at 01:47:20.5 UT, 52 seconds after the initial
Swift BAT trigger (Hurkett et al., GCN 3379). The XRT error circle
(Kennea et al., GCN 3380) falls partially on a known source from the DSS.
We detect no new sources at the Swift XRT position (Kennea et al, GCN
3380). The limiting magnitudes (in 6" radius apertures) in each of the
UVOT filters are as follows:

Filter    Lim_Mag      Lim_mag  Total duration  T_start T_mid
            5sigma       3sigma  (s)             (s)     (s)

V          18.23        18.79   191             52      1853
UVW1       18.97        19.52   210             5722    5827
UVM2       20.29        20.84   921             3763    4739

UVOT only observed GRB050509b in V, UVW1 and UVM2 because it's run of
observations were interrupted by GRB050509b.

The magnitudes are based on preliminary zero-points, measured in
orbit, and will require refinement with further calibration.

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