TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3412
SUBJECT: GRB 050509b: Swift/UVOT follow-up measurements
DATE:    05/05/11 17:25:42 GMT
FROM:    Alexander Blustin at MSSL-UCL  <ajb@mssl.ucl.ac.uk>

A. Breeveld (MSSL), T. Poole (MSSL), E. Rol(LU),
M. Ivanushkina (PSU), S. Rosen (MSSL), M. Still (GSFC),
P. Roming (PSU), N. Gehrels (GSFC), K. Mason (MSSL),
J. Nousek (PSU), on behalf of the Swift UVOT team

Further to the initial Swift UVOT results (C. Hurkett
et al. GCN 3381 and A. Breeveld et al. GCN 3397) we report
the results of co-added, deeper exposures of GRB 050509b
with the Swift Ultra-Violet/Optical Telescope (UVOT) in
the 21 hours following the burst on May 09-10, 2005.

We detect no source at the refined XRT determined
location (12:36:13.9,28:59:01; E. Rol et al., GCN 3395)
nor in the location of the extended source S1 (12:36:13.7,
28:58:57.3; S. Bradley Cenko et al. GCN 3391) in any of
the UVOT filters. The 3-sigma limiting magnitudes are
listed in the following table for the XRT position
(XRT_Lim_Mag) and the S1 position (S1_Lim_Mag). A 6"
aperture was used in all cases.

Filter  XRT_Lim_Mag   S1_Lim_Mag  Total Exp (s) T_range (s)

V	21.1         21.1         5213          50 - 71553
B	21.8         21.8         4696          196 - 69818
U	21.8         21.8         5070          182 - 76713
UVW1	22.3         22.2         6491          169 - 76511
UVM2	22.2         22.2         6493          154 - 75603
UVW2	22.7         22.6         5596          212 - 70726

T_range values are start and stop times between which UVOT
exposures were made, measured w.r.t the BAT trigger time
(Barthelmy et al. GCN 3385).

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