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GCN Circular 25297

Subject
LIGO/Virgo S190808ae: One Coincident Neutrino Candidate from IceCube Search
Date
2019-08-08T23:53:52Z (5 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 S190808ae in a
time range of 1000 seconds [1] centered on the alert event time
(2019-08-08 22:13:01.496 UTC to 2019-08-08 22:29:41.496 UTC) have been
performed.
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 [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].

One track-like event is found in spatial and temporal coincidence with the
gravitational-wave candidate S190808ae calculated from the map circulated in
the 2-Initial notice. This represents an overall p-value of 0.0448 (1.70
sigma) from the generic transient search and an overall p-value of 0.068
(1.49 sigma) for the Bayesian search. These p-values measure the
consistency of the observed track-like events with the known atmospheric
backgrounds.

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.

Properties of the coincident event are shown below.

dt | ra (deg) | dec (deg) | Angular Uncertainty(deg) | p-value(generic
transient) | p-value(bayesian)
-----+--------+---------+------------------------+------------------+--------------------------
 -37 | 216.29 |-15.35     | 0.43                     |0.045
      |0.070

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.
p-value = the p-value for this specific track event from each search.
RA & Dec = Right ascension and declination in degrees quoted in J2000 epoch

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] 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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