[vsnet-grb-info 1858] GRB050726: Swift UVOT observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3698
SUBJECT: GRB050726: Swift UVOT observations
DATE:    05/07/29 15:26:48 GMT
FROM:    Tracey Poole at MSSL  <tsp at mssl.ucl.ac.uk>

T. Poole (MSSL), A. Moretti (OAB), S. T. Holland (GSFC), M. Chester
(PSU), L. Angelini (GSFC-JHU), N. Gehrels (GSFC) on behalf of the Swift
UVOT team

The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of
GRB050726 (Barthlemy et al. GCN 3682) on 26th July 2005 at 05:02:07 UT.
We confirm the detection of a source inside the BAT and XRT error circle
(Barthlemy et al. GCN 3682, A. Moretti et al. GCN 3683) in the V band
only. The source is detected in the initial V band observation, then 
drops below the 3 sigma detection threshold. It is not detected in
the U, B or the UV filters.

The aperture used for all observations was 6 arcsec. The limiting
magnitudes are given to a 3 sigma limit.

V filter

start  exposure mid     magnitude
time   time     time
after           after
burst           burst
(s)    (s)      (s)
123    100      173    17.35+/-0.09 - source detection
298    10       303    17.47        - limiting magnitude
382    10       387    17.43        - limiting magnitude
466    10       471    17.36        - limiting magnitude
551    10       556    17.29        - limiting magnitude
635    10       640    17.49        - limiting magnitude
720    10       725    17.40        - limiting magnitude
9825   900      10275  19.76        - limiting magnitude
21647  900      22097  19.83        - limiting magnitude

Other filters - limiting magnitudes

Filter    start  exposure mid     limiting
           time   time     time    magnitude
           after           after
           burst           burst
           (s)    (s)      (s)
b         269    59       485     19.38
b         4992   1800     6189    21.31
b         29659  12       29665   18.72
u         255    59       216     19.23
u         4124   2700     16888   21.06
uvw1      241    59       457     19.29
uvw1      4020   100      4070    19.49
uvw1      11639  2003     17763   21.44
uvm2      352    68       196     19.41
uvm2      10731  1800     19738   21.48
uvw2      284    89       500     19.88
uvw2      5939   1300     13820   21.62

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

This message may be cited.