GCN Circular 35898

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

On 2024-04-07 at 07:44:57.38 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 0.233 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/139100_34742349.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2024-04-07
Time:  07:44:57.38 UT
RA: 239.63 (+13.20, -15.22 deg  90% PSF containment) J2000
Dec: 39.94 (+18.18, -14.92 deg 90% PSF containment) J2000

The large uncertainty on its directional reconstruction can be explained by the short track length observed, as the event was only partially contained in the detector volume. Nevertheless, this event remains interesting considering that it is an up-going track (indicative of a neutrino origin) with an estimated energy of around 190 TeV, making it potentially astrophysical. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

Given its large uncertainty, there is a large number (>40) of gamma-ray sources within the large 90% uncertainty region of the event, with the closest one listed in the 4FGL-DR4 Fermi-LAT catalog being 4FGL J1557.2+3822, located at RA: 239.31 deg, Dec: 38.38 deg J2000 (1.58 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