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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)
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