GCN Circular 3745
Subject
GRB 050802: Swift/UVOT optical and UV detections
Event
Date
2005-08-03T15:37:09Z (20 years ago)
From
Katie McGowan at MSSL-UCL <km2@mssl.ucl.ac.uk>
K. McGowan (UCL-MSSL), A. Morgan (PSU), K. Mason (PPARC),
T. Kennedy (UCL-MSSL) report on behalf of the Swift/UVOT team:
The Swift/UVOT began observing the afterglow of
GRB 050802 at 2005-08-02T10:15:14, 286 s after the
BAT trigger (Band et al., GCN 3734). In addition to our
reported detection from the initial V filter observations
(McGowan et al., GCN 3739), we now report that we detect
the afterglow in all six filters.
We extracted data using a 6 arcsec radius aperture
centered on the source position (McGowan et al., GCN 3739)
for the optical filters, a 12 arcsec radius for the W1 and
M2 filters, and 4 arcsec for the W2 filter. If the
significance of the source detection was less than 2 sigma
we determined a 3-sigma limiting magnitude.
The detection in UVW2 implies that the Lyman Limit must be blueward
of 2000 A, and we estimate that the burst is at redshift z < 1.2.
We obtain the following photometry of the afterglow candidate:
Filter Exposure (s) T_mid (s) Magnitude Notes
V 100 336 17.07+/-0.09 detection
V 900 12566 20.35+/-0.09 detection
B 10 437 17.66+/-0.20 detection
B 900 36405 21.10+/-0.08 detection
U 10 423 16.82+/-0.24 detection
U 899.79 35498 20.22+/-0.16 detection
W1 10 409 17.08+/-0.29 detection
W1 100 2296 19.22+/-0.23 detection
M2 278 1316 18.79+/-0.26 detection
M2 3753 28197 21.30+/-0.26 detection
W2 268 1240.5 20.73+/-0.27 detection
W2 3481 25890.5 >22.64 3-sig limit
where T_mid 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.