TITLE: GCN CIRCULAR NUMBER: 19787 SUBJECT: IceCube 160806A EHE Neutrino Candidate Event DATE: 16/08/09 16:15:58 GMT FROM: Doug Cowen at Penn State/IceCube D.F. Cowen reports on behalf of the IceCube Collaboration: IceCube detected a candidate cosmic neutrino IceCube-160806A, "AMON ICECUBE EHE 128311 26552458" at 12:21:33.00 UT on 16/08/06 (http://gcn.gsfc.nasa.gov/notices_amon/26552458_128311.amon) The event was an Extremely High Energy (EHE) event with track-like characteristics and it arrived when the IceCube detector was in a normal operating state. EHE events satisfy a combination of high light level and zenith angle that enhances astrophysical signal relative to cosmic-ray-induced backgrounds. In contrast to the other active IceCube high energy track-like neutrino alert stream, known as "HESE," EHE events are not required to start within the IceCube detector fiducial volume. After the initial automated alert, more sophisticated reconstruction algorithms have been applied offline, with the direction refined to RA=122.81d and DEC=-0.8061d (J2000) in revision 1 of this alert. The position uncertainty is estimated from the initial realtime reconstruction from revision 0 of this alert, at 0.1 degrees or 6.7 arcminutes radius (stat. only, 50% containment). Lacking inclusion of systematic effects, we expect this uncertainty underestimates the true uncertainty by roughly a factor of five. We encourage followup 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