TITLE: GCN CIRCULAR NUMBER: 27235 SUBJECT: IceCube-200227A: IceCube observation of a high-energy neutrino candidate event DATE: 20/02/27 10:00:54 GMT FROM: Robert Stein at DESY The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 20/02/27 at 05:36:31.50 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.34 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/133781_21701751.amon ), the detailed angular uncertainty is still being evaluated. At this time we propose to use the preliminary values reported in the GCN Notice: Date: 20/02/27 Time: 05:36:31.50 UT RA: 348.26 deg J2000 Dec: +21.32 deg J2000 Error Radius: 30.80 arcmin (90% containment - statistical) We stress that the reported error estimate only accounts for statistical errors, and that additional systematic uncertainties mean this containment radius is a lower limit. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. The nearest 4FGL sources is 4FGL J2318.2+1915, located at RA 349.56 deg and Dec 19.26 deg a distance of 2.40 deg from the best-fit position. A second source, 4FGL J2323.1+2040, is located at RA 350.79 deg and Dec 20.68 deg, a distance of 2.45 deg from the best-fit position. 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