TITLE: GCN CIRCULAR NUMBER: 35604 SUBJECT: IceCube-240123A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 24/01/23 15:06:40 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum gsommani@icecube.wisc.edu

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

On 2024-01-23 at 11:25:36.05 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 4.1505 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/138890_34080563.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2024-01-23 Time: 11:25:36.05 RA: 357.54 (+1.93, -1.71 deg 90% PSF containment) J2000 Dec: +4.26 (+0.80, -0.76 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 are no Fermi 4FGL or 3FHL catalog sources in the 90% uncertainty region. The nearest gamma-ray source in either catalog is 4FGL J2349.4+0534 at RA: 357.36 deg, Dec: 5.58 deg (1.33 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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