TITLE: GCN CIRCULAR NUMBER: 30957 SUBJECT: IceCube-211023A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 21/10/23 09:47:02 GMT FROM: Dr. Massimiliano Lincetto at Ruhr-Universitaet Bochum <lincetto@astro.rub.de> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2021/10/23 at 08:31:18.31 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 3.2 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/135832_55176071.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2021/10/23 Time: 08:31:18.31 UT RA: +253.30 (+1.05 / -1.08 deg 90% PSF containment) J2000 Dec: -1.72 (+1.16 / -1.11 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. One gamma-ray source, 4FGL J1653.6-0158, is located within the 90% of the error region, 0.27 deg away from the best-fit position. The source is associated with the pulsar PSR J1653-0158. 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