TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3444
SUBJECT: Swift UVOT Observations of GRB 050520
DATE:    05/05/20 21:04:44 GMT
FROM:    Caryl Gronwall at PSU/Swift-UVOT  <caryl@astro.psu.edu>

C. Gronwall (PSU), J. Norris (GSFC), A. Morgan (PSU),
P. Schady (MSSL), N. Gehrels (GSFC), on behalf of the
Swift UVOT Team

INTEGRAL detected GRB 050520 at 00:05:53 UT on 20th May 2005
(Gotz et al., GCN 3430).  Swift executed a Target of Opportunity
observation of the INTEGRAL position.  The Swift Ultra-Violet/Optical
Telescope (UVOT) began observations of GRB050520 at UT 02:13:38,
approximately 2hr 8 minutes after the INTEGRAL detection.

We detect no new source within the Swift XRT error circle
(Kennea et al., GCN Circ. 3443) in any of the UVOT filters
with the following 5 sigma and 3 sigma limits (in 6" radius apertures):



Filter    Lim_Mag      Lim_mag   Total duration (s)   T_range (hr)
           5sigma       3sigma

V          19.84        20.39        3069            5.48 - 13.26
B          21.05        21.60        2699            4.98 - 11.90
U          20.58        21.13        2674            3.62 - 11.65
UVW1       21.30        21.86        3173            3.37 - 13.73
UVM2       21.36        21.91        2824            2.13 - 13.50
UVW2       21.64        22.19        2456            5.23 - 12.12

T_range is time since the INTEGRAL detection.

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

This message may be cited.