TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3397
SUBJECT: Swift UVOT Follow-up Observations of GRB 050509B
DATE:    05/05/09 18:30:50 GMT
FROM:    Pete Roming at PSU  <roming@astro.psu.edu>

A. Breeveld, S. Rosen (MSSL), C. Hurkett (LU), E. Rol(LU), S. Holland (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) we report
the results of co-added, deeper exposures of GRB 050509b with the Swift
Ultra-Violet/Optical Telescope (UVOT) on May 09, 2005.

We detect no source at the XRT determined location (Kennea et al., GCN 3383) in
any of the UVOT filters with the following 5 sigma limits in 6" radius
apertures. Because of the proximity of this position to the galaxy cluster NSC
J123610+285901 the measurements were repeated with a smaller (3.5") aperture.
The measurements are listed in the following table.

Filter    Lim_Mag      Lim_mag           Total duration (s)   T_range (s)
           5sigma (6")  5sigma (3.5")

V          19.0         19.6                 345                51 - 1670
B          19.7         20.3            197.4           196 - 1502
U          19.41        19.44           752.88          182 - 7642

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.