{
  "eventId": "LIGO/Virgo/KAGRA S251108fi",
  "bibcode": "2025GCN.42630....1I",
  "submittedHow": "web",
  "body": "IceCube Collaboration (http://icecube.wisc.edu/) reports:\n\nSearches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S251108fi (GCN 42628) in a time range of 1000 seconds centered on the alert event time (2025-11-08 19:05:08.506 UTC to 2025-11-08 19:21:48.506 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].\n\nOne track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S251108fi calculated from the map circulated in the 4-Update notice. This represents an overall p-value of 0.0076 from the generic transient search and an overall p-value of 0.0421 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 15.12, Dec 9.06 degrees.\n\nThe 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. Additional details and updates will be posted at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch/.\n\nProperties of the coincident event are shown below.\n\n| dt(s) | RA(deg)  | Dec(deg) | Angular uncertainty(deg)| p-value(generic transient)| p-value(Bayesian)     |\n|-------|----------|----------|-------------------------|---------------------------|-----------------------|\n|-242.48   |  15.01  |  9.06  |      1.13           |         0.0076         |       0.0421       |\n\nwhere:\ndt = Time of track event minus time of GW trigger (sec).\nAngular uncertainty = Angular uncertainty of track event: the radius of a circle \n     representing 90% CL containment by area.\np-value = the p-value for this specific track event from each search. \n     Event p-values are provided when the per-event p-value is less than 0.1 in either search.\n\nThe 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\n\n\n[1] M. G. Aartsen et al 2020 ApJL 898 L10\n[2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80\n[3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017\n",
  "circularId": 42630,
  "createdOn": 1762728126619,
  "submitter": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
  "format": "text/markdown",
  "subject": "LIGO/Virgo/KAGRA S251108fi: One counterpart neutrino candidate from IceCube neutrino searches"
}