TITLE: GCN CIRCULAR NUMBER: 35255 SUBJECT: IceCube-231202A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 23/12/04 14:18:52 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum gsommani@icecube.wisc.edu

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

On 2023-12-02 at 17:08:24.09 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 4.4035 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/138632_31747601.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2023-12-02 Time: 17:08:24.09 UT RA: 139.04 (+1.52, -1.96 deg 90% PSF containment) J2000 Dec: +0.37 (+1.11, -1.40 deg 90% PSF containment) J2000

Deployment of updated software delayed the availability of these results, we apologize for the delay. 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 listed in the 4FGL-DR4 Fermi-LAT catalog is inside the 90% uncertainty region. The source is 4FGL J0909.1+0121, located 2.0 deg away from the best-fit position. The source is also listed in the Fermi 3FHL catalog as 3FHL J0909.1+0121.

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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