GCN Circular 3056

Title: GRB050223: ROTSE-III Optical Observations

Smith, D. A. (U. of Michigan) reports on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia responded to
Swift GRB 050223 (Trigger #106709).  An automatic response resulted in a series
of 97 images beginning 7.7 seconds after receipt of the GCN trigger under fair
conditions.  Some light clouds drifted through the field, but the images
calibrated successfully.  The first image began at 23 Feb 2005 03:10:07.74,
61.6 seconds after the burst.  We took 10 5-second, 10 20-second and 67 60-s
exposures.  The images are unfiltered and were calibrated relative to USNO
A2.0. At 18.8 degrees galactic latitude, the source is in a crowded field, and
our limits are adversely effected by source confusion.

Individual images have limiting magnitudes ranging from 16.4-17.1 (for longer
exposures).  Comparison to DSS (second epoch) reveals no new sources within the
3-sigma BAT error circle to a limiting magnitude of 18.0 for co-adds of 10
images taken up to 43 minutes after the burst.  In particular, no new source is
found at the location of the XRT source coordinates (Giommi et al., GCN
Circ. No. 3054).