TITLE:   GCN CIRCULAR
NUMBER:  31618
SUBJECT: IceCube-220221A - IceCube observation of a high-energy neutrino candidate track-like event
DATE:    22/02/21 02:21:22 GMT
FROM:    Marcos Santander at U. Alabama/IceCube  <jmsantander@ua.edu>

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

On 2022-02-21 at 00:42:19.12 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 0.360 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/136348_65788242.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2022-02-21
Time:  00:42:19.12
RA: 287.84 (+4.00, -3.96 deg  90% PSF containment) J2000
Dec: 20.74 (+4.31, -2.26 deg 90% PSF containment) J2000

The event was produced by a short, bright muon track near the bottom of the detector. This topology resulted in a large shift between the initial and revised muon track positions, and an uncertainty region significantly larger than it is typical for these alerts.  

We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

Due to the large uncertainty region and the vicinity of the Galactic Plane, there are 6 sources listed in the Fermi-LAT 4FGL-DR2 catalog within the 90% containment region for the event, the closest being 4FGL J1908.9+2103 (associated with PSR J1908+2105, at 0.65 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