[vsnet-grb-info 1878] Swift/UVOT photometry of GRB050730

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3717
SUBJECT: Swift/UVOT photometry of GRB050730
DATE:    05/07/31 20:48:41 GMT
FROM:    Alexander Blustin at MSSL-UCL  <ajb at mssl.ucl.ac.uk>

A. J. Blustin (UCL-MSSL), S. T. Holland (GSFC/USRA), A. Cucchiara (PSU),
N. White (GSFC), D. Hinshaw (GSFC-SPSYS) on behalf of the Swift/UVOT
team report:

Swift/UVOT began observing GRB050730 at 2005-07-30T20:00:22, 119 s after
the BAT trigger (Holland et al. GCN 3704). A bright source was detected
in the genie image at 14h 08m 17.09s,-3d 46' 18.9" (Holland et al.
GCN 3704). Further analysis of data returned via the Malindi ground
station shows that this source is fading; we report the following V band
lightcurve, including detections significant at greater than 2.8 sigma:

Tmid (s) Exp (s)  Magnitude

170      99.77    17.842 +/- 0.152
300      9.78     17.473 +/- 0.380
384      9.78     17.477 +/- 0.383
468      9.78     16.737 +/- 0.238
553      9.76     16.568 +/- 0.216
637      9.76     17.119 +/- 0.302
722      9.78     16.706 +/- 0.231
3978     99.77    18.274 +/- 0.259
11948    837.11   19.200 +/- 0.150
23520    835.72   20.211 +/- 0.371
35088    843.21   20.286 3-sigma upper limit

Where Tmid is the time after trigger of the mid-point of the
exposure.

Additionally the source was detected at greater than 2.8 sigma 
significance in the B-band in 3 images:

Tmid (s) Exp (s)  Magnitude

271      9.76     18.874 3-sigma upper limit
355      9.77     18.303 +/- 0.321
440      9.77     18.662 3-sigma upper limit
524      9.76     18.492 +/- 0.364
608      9.76     18.766 3-sigma upper limit
693      9.77     18.076 3-sigma upper limit
777      9.76     18.734 3-sigma upper limit
10164    899.77   20.447 +/- 0.208
21737    899.73   21.087 3-sigma upper limit
33309    901.43   21.126 3-sigma upper limit

There was no detection in U or in any of the UV filter exposures.
The upper limits for the summed images in these bands are:

Filter  T range (s) Exp (s)  3-sigma magnitude upper limit

U       252-29724   2490.71  21.747
UVW1    238-28880   3665.12  21.98
UVM2    224-27972   3620.41  22.30
UVW2    281-34660   2765.25  22.40

where T range is the time range post-trigger over which the images
were taken.

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.