TITLE: GCN CIRCULAR NUMBER: 38770 SUBJECT: IceCube-250101A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/01/02 01:23:00 GMT FROM: A. Zegarelli at Ruhr University Bochum azegarelli@icecube.wisc.edu

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

On 2025-01-01 at 21:04:57.73 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 1.9213 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/140312_53817657.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2025-01-01 Time: 21:04:57.73 UT RA: 318.96 (+0.64, -0.63 deg 90% PSF containment) J2000 Dec: -0.93 (+0.49, -0.44 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.

There is one Fermi 4FGL-DR4 or 3FHL catalog source in the 90% uncertainty region: 4FGL J2115.9-0113 at RA: 319.00 deg, Dec: -1.23 deg J2000 (0.3 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

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