TITLE:   GCN CIRCULAR
NUMBER:  26620
SUBJECT: IceCube-191231A: IceCube observation of a high-energy neutrino candidate event
DATE:    19/12/31 21:55:35 GMT
FROM:    Marcos Santander at U. Alabama/IceCube  <jmsantander@ua.edu>

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

On 19/12/31 at 11:00:06.08 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 1.56 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/133572_82361476.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 19/12/31 
Time: 11:00:06.08 UT
RA: 46.36 (+ 4.27 - 3.47 deg 90% PSF containment) J2000
Dec: 20.42 (+ 2.11 - 2.80 deg 90% PSF containment) J2000

We note that this event had a topology with a short distance traversed through the detector, and consequently the localization uncertainty of this event is significantly larger than first reported. We nonetheless encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

There are three Fermi 4FGL sources within 3 degrees of the best-fit position, one of which is also listed in the Fermi 3FHL catalog. The nearest gamma-ray source in either catalog is 4FGL J0258.1+2030 at RA: 44.54 deg, Dec: 20.51 deg (1.71 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