GCN Circular 3165
Subject
GRB050401: ROTSE-III Detection of Prompt Optical Counterpart
Event
Date
2005-04-01T18:49:02Z (21 years ago)
From
Eli Rykoff at U of Michigan/ROTSE <erykoff@umich.edu>
E. S. Rykoff, S. A. Yost, D. A. Smith (Umich) report on behalf of the
ROTSE collaboration:
ROTSE-IIIa, located at Siding Spring Observatory, Australia responded to
Swift GRB050401 (Trigger #113120). An automated response produced
images beginning 6.2 seconds after the GCN trigger under good
conditions. The first image was taken at 01 Apr 14:20:39.2 UT, 33
seconds after the updated burst time as reported by Barbier et al (GCN
3162). We took ten 5 second, ten 20 second and sixty 60 s exposures,
and imaging is ongoing. The images are unfiltered and were calibrated
relative to USNO A2.0.
Individual images have limiting magnitudes ranging from 16.0-17.3. We
compared sets of 10 co-added frames to the DSS (second epoch). In our
first co-added set of images we have a marginal detection of a source
consistent with the XRT position (GCN 3161) and the candidate reported
by McNaught & Price (GCN 3163). The source is at 17.0+/-0.2 for a 151
second co-add starting at 14:20:39.2 UT, with a limiting magnitude of
17.4. We do not detect any significant flux in our following images, to
a limiting magnitude of 17.9/18.4 for sets of images beginning at
14:28:22.3 UT/14:39:57 UT.
We also note that our first 5-s image was taken coincidentally with the
end of the gamma-ray emission detected by Swift (GCN 3162). We do not
detect significant flux to a limiting magnitude of 16.0.