# GCN Circular 26460

**Subject**

LIGO/Virgo S191216ap: 1 counterpart neutrino candidate from IceCube neutrino searches

**Date**

2019-12-16T23:52:37Z (4 years ago)

**From**

Raamis Hussain at IceCube <raamis.hussain@icecube.wisc.edu>

```
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)
```