TITLE: GCN CIRCULAR NUMBER: 26460 SUBJECT: LIGO/Virgo S191216ap: 1 counterpart neutrino candidate from IceCube neutrino searches DATE: 19/12/16 23:52:37 GMT FROM: Raamis Hussain at 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 S191216ap in a time range of 1000 seconds [1] centered on the alert event time (21:25:18.473 UTC to 21:41:58.473 UTC) have been performed. Up until 21:33:21 UTC IceCube was collecting good quality data, at which point power issues at the experimental site caused issues with data quality. Only neutrino candidates collected before this time are considered. 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 [2]. 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 in the significance estimate, such as GW source distance [3]. 1 track-like event is found in spatial and temporal coincidence with the gravitational-wave Candidate S191216ap calculated from the map circulated in the 2-Initial notice. This represents an overall p-value of 0.104 (1.26 sigma) from the generic transient search and an overall p-value of 0.0059 (2.52 sigma) for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds. Both analyses assume 100% livetime during the search window; the statistical significances are therefore lower limits. The reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. Properties of the coincident event are shown below. dt ra(deg) dec(deg) Angular Uncertainty(deg) p-value(generic transient) p-value(binary merger) -------------------------------------------------------------------------------------------------------------------- -43s 329.19 4.53 4.07 0.219 0.0059 where: dt = Time offset (sec) of track event with respect to GW trigger. Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. Pvalue = the pvalue 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] Baret et al., Astroparticle Physics 35, 1 (2011) [2] PoS(ICRC2019)918, Braun et al., Astroparticle Physics 29, 299 (2008) [3] Bartos et al. arXiv:1810.11467 (2018) and Countryman et al.arXiv:1901.05486 (2019)