GCN Circular 26788

J. Alvarez-Muniz, F. Pedreira, E. Zas (IGFAE & University of Santiago de
Compostela, Spain),
K. H. Kampert & M. Schimp (University of Wuppertal, Germany)
on behalf of the Pierre Auger Collaboration.

In response to:
LIGO/Virgo GW trigger S200115j
T0=2020-01-15  04:23:09 UTC

We searched for Ultra-High-Energy (UHE) neutrinos with energies
above ~ 1e17 eV in data collected with the Surface Detector (SD)
of the Pierre Auger Observatory in a [-500,500] second interval
about the LIGO-Virgo trigger S200115j as well as in a 24 hr time
interval following the event.

NO events survived the cuts applied to reject the background due
to UHE Cosmic Rays i.e. NO neutrino candidates were detected.

The field of view (fov) where the SD of Auger is sensitive to UHE
neutrinos (corresponding to inclined directions with respect to the
vertical relative to the ground) was PARTIALLY COINCIDENT (51.8%)
at the time T0 of the merger alert, with the latest LIGO/Virgo 90%
localization region (bayestar.fits.gz),
achieving a MAXIMUM OVERLAP (56.1%) at approximately T0+23.33 hours.

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The Pierre Auger Observatory is an UHE Cosmic Ray detector
located in the Mendoza Province in Argentina. It consists of
an array of Water Cherenkov detectors spread over a total surface
of 3000 km^2 arranged in a triangular grid of 1.5 km side as well
as Fluorescence telescopes and other systems
(see 10.1016/j.nima.2015.06.058 for more information).
For neutrino searches with Auger, please refer to:
https://iopscience.iop.org/article/10.1088/1475-7516/2019/10/022
https://iopscience.iop.org/article/10.1088/1475-7516/2019/11/004