TITLE:   GCN CIRCULAR
NUMBER:  35365
SUBJECT: LIGO/Virgo/KAGRA S231215i: 3 counterpart neutrino candidate events from an IceCube neutrino search
DATE:    23/12/15 22:31:26 GMT
FROM:    acz2122@columbia.edu

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

We have performed a search for track-like muon neutrino events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S231215i in a time range of 1000 seconds centered on the alert event time (2023-12-15T02:22:01 UTC to 2023-12-15T02:38:41 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].  

Three track-like events are found in spatial and temporal coincidence with the gravitational-wave candidate S231215i calculated from the map circulated in the S231215i-2-Preliminary notice, although not in coincidence with each other. This represents an overall p-value of 0.0039 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 events are shown below:

 dt(s)     RA(deg)       Dec(deg)    Angular uncertainty(deg)  p-value(Bayesian)
-------------------------------------------------------------------------------------
-199.53    311.05         +33.46           2.774                   0.0063
-153.98    223.68          +7.51           1.723                   0.0304
-322.42    220.21         +25.97           1.374                   0.0398

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