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GCN Circular 31126

Subject
IceCube-211125A: IceCube observation of a high-energy neutrino candidate track-like event
Date
2021-11-25T16:13:00Z (2 years ago)
From
Cristina Lagunas Gualda at DESY <cristina.lagunas@desy.de>
The IceCube Collaboration (http://icecube.wisc.edu/) reports:

On 21/11/25 at 06:22:21.56 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 1.973 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/135936_74588253.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 21/11/25
Time: 06:22:21.56 UT
RA: 43.59 (+ 3.13 - 2.71 deg 90% PSF containment) J2000
Dec: 22.59 (+ 1.54 - 2.53 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 two Fermi-LAT 4FGL sources inside the 90% localization region. The nearest source is 4FGL J0248.0+2232, located at RA 42.01 deg and Dec 22.54 deg (J2000), at a distance of 1.46 degrees from the best-fit location.

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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