TITLE:   GCN CIRCULAR
NUMBER:  27787
SUBJECT: IceCube-200523A - IceCube observation of a high-energy neutrino candidate event
DATE:    20/05/23 04:00:22 GMT
FROM:    Erik Blaufuss at U. Maryland/IceCube  <blaufuss@umd.edu>

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

On 20/05/23 at 02:30:07.59 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 4.9 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/134116_58596690.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/05/23 
Time: 02:30:07.59 UT
RA: 338.64 (+10.77 -6.07 deg 90% PSF containment) J200
Dec: 1.75 (+1.84 -3.54 deg 90% PSF containment) J2000

The larger than usual error region in RA from the offline reconstructions is being investigated.   

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

Ten sources from the Fermi 4FGL catalog are inside the 90% localization region, the closest being 4FGL J2227.9+0036 located at RA 336.98 deg and Dec 0.62 deg (at a distance of 2.01 degrees from the best-fit location).

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