TITLE: GCN CIRCULAR NUMBER: 34906 SUBJECT: LIGO/Virgo/KAGRA S231029y: One counterpart neutrino candidate from IceCube neutrino searches DATE: 23/10/29 16:04:02 GMT FROM: Aswathi Balagopal V. at UW-Madison/IceCube 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 S231029y in a time range of 1000 seconds centered on the alert event time (2023-10-29 11:06:48.000 UTC to 2023-10-29 11:23:28.000 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]. One track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S231029y calculated from the map circulated as S231029y-4-Update. This represents an overall p-value of 0.008 from the generic transient search and an overall p-value of 0.998 for the Bayesian search. These p-values measure the consistency of the observed track-like event 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 neutrino and GW skymap is RA 165.79, Dec -31.17 degrees. The 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 event are shown below. dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(generic transient) p-value(Bayesian) ----------------------------------------------------------------------------------------------------- -214.74 165.79 -31.17 0.43 0.008 0.998 ... 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