GCN Circular 39176

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