TITLE: GCN CIRCULAR NUMBER: 33354 SUBJECT: IceCube-230220A - IceCube observation of a high-energy neutrino candidate DATE: 23/02/20 15:52:22 GMT FROM: Dr. Massimiliano Lincetto at Ruhr-Universitaet Bochum The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2023-02-20 at 07:39:10.8 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 2.521 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/137668_51133257.amon), attempts to use a more sophisticated algorithm that provides refined position and error estimates encountered issues. Given the topology of the light deposition in the detector, we estimate that the initial direction listed below still provides a good characterization of the event. Date: 2023-02-20 Time: 07:39:10.8 UT RA: 359.33 deg (J2000) Dec: +3.35 deg (J2000) Error radius: 0.51 deg (90%, statistical error only) We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No gamma-ray sources listed in the 4FGL-DR3 or 3FHL Fermi-LAT catalogs are located within the 90% error radius of the candidate neutrino event. The nearest source is 4FGL J2359.3+0215, 1.2 deg away from the best-fit event 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