GCN Circular 23375

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

On 23 October 2018 UTC IceCube detected a track-like, very-high-energy 
event with a high probability of being of astrophysical origin. The 
event was identified by the ��Extremely High Energy (EHE) track event 
selection.�� The IceCube detector was in a normal operating state. EHE 
events typically have a neutrino interaction vertex that is outside the 
detector, produce a muon that traverses the detector volume, and have a 
high light level (a proxy for energy).

After the initial automated alert 
(https://gcn.gsfc.nasa.gov/notices_amon/53411354_131653.amon), more
sophisticated reconstruction algorithms have been applied offline, with 
the direction refined to:

Date: 18/10/23

Time: 16:37:32.65 UTC
RA: 270.18 (-1.70,+2.00 deg ��90% PSF containment) J2000
Dec: -8.57 ��(-1.30,+1.25 deg 90% PSF containment) J2000

The closest sources to this position among Fermi-LAT catalogs 3FGL, 
2FGL, and 3FGL and Roma-BZCat is the unassociated source 3FGL 
J1804.5-0850 (1.3 degrees from best fit refined direction). ��We 
encourage follow-up of this alert by ground and space-based instruments 
to help identify a possible astrophysical source for the candidate neutrino.


The original GCN Notice contained an incorrect statement that ���this EHE 
event is the same as the previously reported HESE event.����� This is a 
unique EHE alert trigger and unrelated to previously reported HESE alerts.


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