TITLE:   GCN CIRCULAR
NUMBER:  21756
SUBJECT: LIGO/Virgo G299232: WHT non-detection u-band optical transient
DATE:    17/08/29 20:33:05 GMT
FROM:    Peter Jonker at SRON/RU  <p.jonker@sron.nl>

P.G. Jonker (SRON/RU), M. Fraser (UCD), S. Nissanke (RU), R.P. Fender (Oxford),
J. Broderick (ASTRON),  A. Rowlinson (UvA, ASTRON), R.A.M.J. Wijers (UvA), B.W.
Stappers (Manchester) report on behalf of the LOFAR Transients Key Science
project:

On Aug, 29, 2017, starting at 00:45 (UTC), we obtained a u'-band image
with an exposure time of 300 sec, with the ACAM instrument mounted on
the William Herschel Telescope on La Palma (Spain) of the optical
transient reported by Emery et al. GCN21733 (see also Tomasella et
al. GCN 21745). We do not detect a source at the reported position
down to an SDSS-based AB limiting magnitude of u'>24.5 based on the
faintest sources visible in the field. This implies a fading of more
than a factor 350 in about 36.75 hours (assuming the time unit in GCN
21733 is UT).