GCN Circular 41818

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

IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 250911A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/141344_29341777.amon) in a time range of 1000 seconds centered on the alert event time (2025-09-11 04:20:17.140 UTC to 2025-09-11 04:36:57.140 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, two track-like events are found within the 90% containment region of IceCube-Cascade 250911A. We find that these additional 2 events are well described by atmospheric background expectations, with a p-value of 0.01. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.3e-01 to 6.1e+00 GeV cm^-2 within the 90% spatial containment region of IceCube-Cascade 250911A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 3e+06 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2025-09-10 04:28:37.140 UTC to 2025-09-12 04:28:37.140 UTC). In this case, we report a p-value of 0.23, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.5e-01 to 6.2e+00 GeV cm^-2 within the 90% spatial containment of IceCube-Cascade 250911A in a 2 day time window. 

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.

[1] IceCube Collaboration, R. Abbasi  et al., ApJ 910 4 (2021)