TITLE: GCN CIRCULAR NUMBER: 37625 SUBJECT: IceCube-240929A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 24/09/29 14:52:14 GMT FROM: Erik Blaufuss at University of Maryland, College Park blaufuss@umd.edu

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

On 2024-09-29 at 09:55:54.03 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.7553 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/139912_46959751.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2024-06-29 Time: 09:55:54.03 UT RA: 180.66 (+0.57, -0.71 deg 90% PSF containment) J2000 Dec: 18.92 (+0.55, -0.54 deg 90% PSF containment) J2000

No Fermi 4FGL or 3FHL catalog source are in the 90% uncertainty region. However, given the promising characteristics of the candidate neutrino event, we encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source associated with it.

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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