TITLE: GCN CIRCULAR NUMBER: 39176 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Two counterpart neutrino candidates from IceCube neutrino searches DATE: 25/02/06 22:36:52 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison thwaites@wisc.edu

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

Searches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S250206dm in a time range of 1000 seconds centered on the alert event time (2025-02-06 21:17:10.436 UTC to 2025-02-06 21:33:50.436 UTC) have been performed [1,2]. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap. The second uses 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 significance estimate [3].

Two track-like events are found in spatial and temporal coincidence with the gravitational-wave candidate S250206dm calculated from the map circulated in the 3-Initial notice. This represents an overall p-value of 0.008 from the generic transient search and an overall p-value of 0.011 for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not trials corrected for multiple GW events). The most probable multi-messenger source direction based on the neutrinos and GW skymap is RA 149.15 degrees, Dec -17.90 degrees.

The two reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in the Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. The false alarm rate of these coincidences can be obtained by multiplying the p-values with their corresponding GW trigger rates. Further details are available at https://gcn.nasa.gov/missions/icecube.

Properties of the coincident events are shown below. We encourage follow-up observations of both locations.

dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(generic transient) p-value(Bayesian) ----------------------------------------------------------------------------------------------------- 289.12 149.16 -17.94 0.43 0.008 0.032 -109.85 354.59 32.79 1.42 0.222 0.018

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 each 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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