TITLE: GCN CIRCULAR NUMBER: 38993 SUBJECT: LIGO/Virgo/KAGRA S250105bn: 1 counterpart neutrino candidate event from an IceCube neutrino search DATE: 25/01/20 02:12:05 GMT FROM: Zsuzsa Marka at IceCube/Columbia University zsuzsa@astro.columbia.edu

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 S250105bn in a time range of 1000 seconds centered on the alert event time (2025-01-05 08:07:30 UTC to 2025-01-05 08:24:10 UTC) [1,2]. During this time period, IceCube was collecting good quality data. The results are released with a delay due to software misconfiguration.

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 S250105bn calculated from the map circulated in the S250105bn-2-Preliminary notice. This represents an overall p-value of 0.0051 for the Bayesian search. The p-value measures the consistency of the observed track-like event 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) ------------------------------------------------------------------------------------- 107.15 352.11 -16.39 4.87 0.0051

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 p-value for this 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

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