GCN Circular 34616

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 S230904n in a time range of 1000 seconds centered on the alert event time (2023-09-04 05:01:53.000 UTC to 2023-09-04 05:18:33.000 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 S230904n calculated from the map circulated in the 3-Initial notice. This represents an overall p-value of 12% from the generic transient search and an overall p-value of 0.4% 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 348.40, Dec 37.26 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 events are shown below.

dt(s) 	RA(deg) 	Dec(deg) 	Angular uncertainty(deg) 	p-value (generic transient) 	p-value (Bayesian)
----------------------------------------------------------------------------------------------------------------------------------------------------
263 	348.89 	 	36.55 	 	3.16  	 	 	 	 	 	0.1625 	 	 	 	 	 	 	0.0037

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