[vsnet-grb-info 23111] LIGO/Virgo S190728q: Third update on neutrino search with IceCube

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25210
SUBJECT: LIGO/Virgo S190728q: Third update on neutrino search with IceCube
DATE:    19/07/28 22:28:20 GMT
FROM:    Raamis Hussain at IceCube  <raamis.hussain at icecube.wisc.edu>

IceCube Collaboration (http://icecube.wisc.edu/) reports:

This is an update of GCN 25197 including updated p-values for the map
circulated in the 5-Update GCN notice.

Searches for track-like muon neutrino events detected by IceCube consistent
with the sky localization of gravitational-wave candidate S190728q in a
time range of 1000 seconds [1] centered on the alert event time (2019-07-28
06:36:50.529 UTC to 2019-07-28 06:53:30.529 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 S190728q calculated from the map circulated in
the 5-Update notice. This represents an overall p-value of 0.014 (2.21
sigma) from the generic transient search and an overall p-value of 0.010
(2.33 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 Bayesian binary merger
search, while it is not taken into account in the generic transient
point-like source search.

Properties of the coincident events are shown below.

   dt|ra (deg)|dec (deg)|Angular Uncertainty(deg)|p-value
(bayesian)|p-value(generic transient)
-----+--------+---------+------------------------+------------------+--------------------------
 -360|312.87  |5.85     |4.81                    |0.010             |0.016

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 at 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)