TITLE: GCN CIRCULAR NUMBER: 33552 SUBJECT: IceCube-230401A: IceCube observation of a high-energy neutrino candidate DATE: 23/04/01 17:13:32 GMT FROM: Cristina Lagunas Gualda at DESY cristina.lagunas@desy.de

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

On 23-04-01 at 16:14:18.91 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 4.11 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/137794_38132005.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 23-04-01 Time: 16:14:18.91 UT RA: 8.17 (+4.26/-2.91 deg 90% PSF containment) J2000 Dec: +1.94 (+2.44/-1.96 deg 90% PSF containment) J2000

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

There are several Fermi 4FGL or 3FHL catalog sources in the 90% uncertainty region. The nearest gamma-ray source is 4FGL J0038.1+0012 at RA: 9.54 deg, Dec: 0.21 deg (2.20 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