GCN Circular 30862

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

On 2021-09-22 at 18:17:20.948 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 0.1472 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/135736_30987826.amon), more  
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2021-09-22
Time: 18:17:20.948
RA: 60.73 (+0.96/-0.66 deg 90% PSF containment) J2000
Dec: -4.18 (+0.42/-0.55 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 J0357.2-0319 / 3FHL J0357.3-0316 at RA: 59.32 deg, Dec: -3.32 deg (1.64 deg away from the best-fit event position). The source is classified as having a possible blazar origin. 

This neutrino candidate event has an estimated neutrino energy of ~750 TeV and an estimated signalness of >90%, making it one of the most interesting neutrino alerts issued in the last year.  

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