GCN Circular 24028

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

On March 31, 2019, IceCube detected a track-like, very-high-energy event with a high probability of being produced by a muon neutrino of astrophysical origin. The event was identified by the High Energy Starting Event (HESE) track selection. The IceCube detector was in a normal operating state. HESE tracks have a neutrino interaction vertex inside the detector and produce a muon that only partially traverses the detector volume, and have a high light level (a proxy for energy).

After the initial automated alert was issued, visual inspection of the event revealed that the online directional reconstruction reported in the original GCN (https://gcn.gsfc.nasa.gov/notices_amon/15947448_132379.amon) was very incorrect, biased by the topology of the event. More sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2019/03/31 
Time: 06:55:43.44 UT 
RA: 337.68deg (+0.23deg -0.34deg 90% PSF containment) J2000
Dec:  -20.70deg (+0.30deg -0.48deg 90% PSF containment) J2000

Additionally, given the large deposited energy observed in this event (one of the highest observed so far), it has a very high likelihood of being of astrophysical origin. We strongly 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 catalog sources in the 90% region. The nearest source is 1RXS J223249.5-202232 (4FGL J2232.6-2023) at RA: 338.1725deg, Dec: -20.3909deg.

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 .