TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3733
SUBJECT: GRB050801: Swift/UVOT Optical and UV detections
DATE:    05/08/02 07:57:28 GMT
FROM:    Alexander Blustin at MSSL-UCL  <ajb@mssl.ucl.ac.uk>

A. J. Blustin (UCL-MSSL), D. Band (GSFC), S. Hunsberger (PSU),
C. Gronwall (PSU), M. Carter (UCL-MSSL), P. Smith (UCL-MSSL)
on behalf of the Swift/UVOT team report:

The Swift/UVOT began observing the afterglow of GRB050801 at
2005-08-01T18:32:00, 238 s after the BAT trigger (Band et al.,
GCN 3725). The afterglow was detected in all six optical and
UV filters at a position (J2000, corrected to the DSS
coordinates) of:

RA  13:36:35 (+/- 1 arcsec)
DEC -21:55:41 (+/- 1 arcsec)

We give two lightcurve points for each filter in the table
below so that decay slopes may be determined.

Filter  T_mid  Exp     Magnitude

V       244    9.78    15.9 +/- 0.2
V       919    9.77    17.9 +/- 0.8

B       215    9.78    16.0 +/- 0.1
B       890    9.78    18.0 +/- 0.4

U       201    9.78    15.20 +/- 0.09
U       961    9.76    17.2 +/- 0.3

UVW1    187    9.78    15.5 +/- 0.1
UVW1    11316  899.77  20.1 +/- 0.3

UVM2    173    9.78    16.0 +/- 0.2
UVM2    6590   337.06  20.6 +/- 0.9

UVW2    230    9.78    17.4 +/- 0.4
UVW2    4524   670.56  21.0 +/- 0.4

Where Tmid is the midpoint of the exposure post-trigger in seconds.

The magnitudes are based on preliminary zero points, measured in
orbit, and will require refinement with further calibration. All
magnitudes are uncorrected for Galactic reddening.