TITLE: GCN CIRCULAR NUMBER: 21496 SUBJECT: LIGO/Virgo G296853: Pierre Auger Observatory neutrino follow-up DATE: 17/08/16 13:42:51 GMT FROM: Jaime Alvarez-Muniz at Pierre Auger Observatory J. Alvarez-Muniz, F. Pedreira, E. Zas (Univ. Santiago de Compostela, Spain), K. H. Kampert & M. Schimp (Bergische Universitat, Wuppertal, Germany) on behalf of the Pierre Auger Collaboration. In response to the LIGO/Virgo GW trigger G296853 (GCN #21431, T0=2017-08-09 08:28:21.747 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 G296853 as well as 1 day after it. 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 NOT coincident with the LIGO 90% localization region at the time T0 of the merger alert. The LIGO 90% localization region maximally overlapped with the Auger fov for the first time ~ 7 hours after the merger. 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 from GW events with Auger, please refer to: https://journals.aps.org/prd/pdf/10.1103/PhysRevD.94.122007