TITLE: GCN CIRCULAR NUMBER: 40122 SUBJECT: IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/08 19:18:55 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison thwaites@wisc.edu

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-250406A (https://gcn.nasa.gov/circulars/40103) in a time range of 1000 seconds centered on the alert event time (2025-04-06 22:42:15.340 UTC to 2025-04-06 22:58:55.340 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250406A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250406A is 1.4e-01 GeV cm^-2 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 9e+04 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-05 22:50:35.340 UTC to 2025-04-07 22:50:35.340 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250406A is 1.6e-01 GeV cm^-2 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)

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