TITLE: GCN CIRCULAR NUMBER: 23605 SUBJECT: IceCube-190104A - IceCube observation of a high-energy neutrino candidate event DATE: 19/01/04 11:46:14 GMT FROM: Claudio Kopper at IceCube/U of Alberta The IceCube Collaboration (http://icecube.wisc.edu/) reports: On January 4, 2019, IceCube detected a track-like, very-high-energy event with a high probability of being of astrophysical origin. The event was identified by the High Energy Starting Event (HESE) track selection. The IceCube detector was in a normal operating state. HESE tracks have a neutrino interaction vertex inside the detector and produce a muon that only partially traverses the detector volume, and have a high light level (a proxy for energy). An inspection of the event does not reveal any feature to rule out this event as an astrophysical candidate. However, this event has a light level that is right above the analysis threshold so there is a non-negligible probability that this event is an atmospheric background. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon/68269692_131999.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2019/01/04 Time: 08:34:38.23 UT RA: 357.98 [-2.1,+2.3] (deg 90% PSF containment) J2000 Dec: -26.65 [-2.5,+2.2] (deg 90% PSF containment) J2000 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