GCN Circular 41867

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

We have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250918aw in a time range of 1000 seconds centered on the alert event time (2025-09-18 07:55:35 UTC to 2025-09-18 08:12:15 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the statistical significance estimation [3].  

One track-like event was found in spatial and temporal coincidence with the gravitational-wave candidate S250918aw calculated from the map circulated in the S250918aw-2-Preliminary notice. This represents an overall p-value of 0.00023 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). 

Further details are available at https://gcn.nasa.gov/missions/icecube and at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch.

Properties of the coincident event are shown below:

 dt(s)     RA(deg)       Dec(deg)    Angular uncertainty(deg)  p-value(Bayesian)
-------------------------------------------------------------------------------------
-74.35 		159.8 		44.3 		0.66 			0.00023


where:
dt = Time of track event minus time of GW trigger (sec)
Angular uncertainty = Angular uncertainty of track event: the radius of a circle 
     representing 90% CL containment by area.
p-value = the individual p-value for the specific track event from this search.

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] M. G. Aartsen et al 2020 ApJL 898 L10
[2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80
[3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017