TITLE: GCN CIRCULAR NUMBER: 22105 SUBJECT: IceCube-171106A - IceCube observation of a high-energy neutrino candidate DATE: 17/11/06 22:37:07 GMT FROM: Ignacio Taboada at Georgia Inst of Tech The IceCube Collaboration (http://icecube.wisc.edu/) reports: On November 6, 2017 IceCube detected a track-like, very-high-energy event with a high probability of being of astrophysical origin. The event was identified by the Extremely High Energy (EHE) track event selection. The IceCube detector was in a normal operating state. EHE events typically have a neutrino interaction vertex that is outside the detector and produce a muon that traverses the detector volume, and have a high light level (a proxy for energy). After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon/17569642_130214.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 17/11/06 (yy/mm/dd) Time: 18:39:39.21 UT RA: 340.00 (-0.50/+0.70 deg 90% PSF containment) J2000 Dec: +7.40 (-0.25/+0.35 deg 90% PSF containment) J2000 Initial offline analysis of this event indicates that the event is consistent with being produced by a neutrino with energy in excess of 1 PeV. The initially reported signalness and energy values are likely underestimated. As indicated in the initial notice, the neutrino candidate is temporally close to Fermi GBM trigger 531686417. However, recently, Fermi GBM has been triggering frequently on a galactic source that is not spatially coincident with the event reported here. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu