GCN Circular 21522

M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (IFIC & APC), D. Dornic (CPPM/CNRS), A. Kouchner (APC/Universite Paris Diderot), T.
Pradier (IPHC/Universite de Strasbourg) report on behalf of the ANTARES Collaboration:

Using on-line data from the ANTARES detector, we have performed a follow-up analysis of the recently reported LIGO/Virgo G298048 event
using the updated Bayestar-HLV probability map at event time. The ANTARES visibility at the time of the alert together with the 90% contour 
of the probability map are shown in: https://www.cppm.in2p3.fr/~dornic/events/G298048/170817_visi2.png <https://www.cppm.in2p3.fr/~dornic/events/G298048/170817_visi2.png> (gwantares/GW@ANT31). The 90% 
contour of the probability map is outside of the ANTARES field-of-view at the alert time.

No up-going muon neutrino candidate events were recorded in the ANTARES sky during a +/- 500s time-window centered on the G298048 event
time. The expected number of atmospheric background events in the region visible by ANTARES is ~1.1e-2 in the +/- 500s time window. An
extended search during +/- 1 hour gives no up-going neutrino coincidence.

An estimate of the upper limit on the associated neutrino fluence will be sent in a subsequent circular.

ANTARES, being installed in the Mediterranean Deep Sea, is the largest neutrino detector in the Northern Hemisphere.  It is primarily
sensitive to astrophysical neutrinos in the TeV-PeV energy range.  At 10 TeV, the median angular resolution for muon neutrinos is below 0.5 degrees.  
In the range 1-100 TeV, ANTARES has the best sensitivity to a large fraction of the Southern sky.