Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817
with ANTARES, IceCube, and the Pierre Auger Observatory
ANTARES Collaboration, IceCube Collaboration, The Pierre Auger Collaboration,
and LIGO Scienti
fi
c Collaboration and Virgo Collaboration
(
See the end matter for the full list of authors.
)
Received 2017 October 15; revised 2017 November 9; accepted 2017 November 10; published 2017 November 29
Abstract
The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary
neutron star inspiral. A short gamma-ray burst
(
GRB
)
that followed the merger of this binary was also recorded by
the
Fermi
Gamma-ray Burst Monitor
(
Fermi
-GBM
)
, and the Anti-Coincidence Shield for the Spectrometer for the
International Gamma-Ray Astrophysics Laboratory
(
INTEGRAL
)
, indicating particle acceleration by the source.
The precise location of the event was determined by optical detections of emission following the merger. We
searched for high-energy neutrinos from the merger in the GeV
–
EeV energy range using the A
NTARES
, IceCube,
and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within
±
500 s
around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We
further carried out an extended search in the direction of the source for high-energy neutrinos within the 14 day
period following the merger, but found no evidence of emission. We used these results to probe dissipation
mechanisms in relativistic out
fl
ows driven by the binary neutron star merger. The non-detection is consistent with
model predictions of short GRBs observed at a large off-axis angle.
Key words:
gamma-ray burst: general
–
gravitational waves
–
neutrinos
1. Introduction
The observation of binary neutron star mergers with multiple
cosmic messengers is a unique opportunity that enables the
detailed study of the merger process and provides insight into
astrophysical particle acceleration and high-energy emission
(
e.g., Faber & Rasio
2012
; Bartos et al.
2013
; Berger
2014
;
Abbott et al.
2017a
)
. Binary neutron star mergers are prime
sources of gravitational waves
(
GWs; e.g., Abadie et al.
2010
)
,
which provide information on the neutron star masses and spins
(
e.g., Veitch et al.
2015
)
. Kilonova
/
macronova observations of
the mergers provide further information on the mass ejected by
the disruption of the neutron stars
(
e.g., B. Abbott et al. 2017,
in preparation; Metzger
2017
)
.
Particle acceleration and high-energy emission by compact
objects are currently not well understood
(
e.g., Mészáros
2013
;
Kumar & Zhang
2015
)
and could be deciphered by combined
information on the neutron star masses, ejecta mass, and
gamma-ray burst
(
GRB
)
properties, as expected from multi-
messenger observations. In particular, the observation of high-
energy neutrinos would reveal the hadronic content and
dissipation mechanism in relativistic out
fl
ows
(
Waxman &
Bahcall
1997
)
. A quasi-diffuse
fl
ux of high-energy neutrinos of
cosmic origin has been identi
fi
ed by the IceCube observatory
(
Aartsen et al.
2013a
,
2013b
)
. The source population producing
these neutrinos is currently not known.
On 2017 August 17, the Advanced LIGO
(
Aasi et al.
2015
)
and
Advanced Virgo
(
Acernese et al.
2015
)
observatories recorded a
GW signal, GW170817, from a binary neutron star inspiral
(
Abbott
et al.
2017b
)
. Soon afterward,
Fermi
-GBM and
INTEGRAL
detected a short GRB, GRB 170817A, from a consistent location
(
Abbott et al.
2017a
; Goldstein et al.
2017
; Savchenko et al.
2017
)
.
Subsequently, ultraviolet, optical, and infrared emission was
observed from the merger, consistent with kilonova
/
macronova
emission. Optical observations allowed the precise localization of
the merger in the galaxy NGC 4993, at equatorial coordinates
a
=
()
J2000.0 13 09 48.085
hm
s
,
d
=- ¢
()
J2000.0
23 22 53. 34
3
(
Abbott et al.
2017c
; Coulter et al.
2017a
,
2017b
)
,andata
distance of
∼
40 Mpc. At later times, X-ray and radio emissions
were also observed
(
Abbott et al.
2017c
)
, consistent with the
expected afterglow of a short GRB at high viewing angles
(
e.g.,
Abbott et al.
2017a
)
.
High-energy neutrino observatories continuously monitor
the whole sky or a large fraction of it, making them well suited
for studying emission from GW sources, even for unknown
source locations or for emission prior to or after the GW
detection
(
Adrián-Martínez et al.
2016a
; Albert et al.
2017a
)
.It
is also possible to rapidly analyze the recorded data and inform
other observatories in the case of a coincident detection,
signi
fi
cantly reducing the source localization uncertainty
compared to that provided by GW information alone.
In this Letter, we present searches for high-energy neutrinos
in coincidence with GW170817
/
GRB 170817A by the three
most sensitive high-energy neutrino observatories:
(
1
)
the
A
NTARES
neutrino telescope
(
hereafter A
NTARES
; Ageron et al.
2011
)
, a 10 megaton-scale underwater Cherenkov neutrino
detector located at a depth of 2500 m in the Mediterranean Sea;
(
2
)
the IceCube Neutrino Observatory
(
hereafter IceCube;
Aartsen et al.
2017
)
, a gigaton-scale neutrino detector installed
1500 m deep in the ice at the geographic South Pole,
Antarctica; and
(
3
)
the Pierre Auger Observatory
(
hereafter
Auger; Aab et al.
2015b
)
, a cosmic-ray air-shower detector
consisting of 1660 water-Cherenkov stations spread over an
area of
∼
3000 km
2
. All three detectors joined the low-latency
multi-messenger follow-up effort of LIGO
–
Virgo starting with
LIGO
’
s second observation run, O2.
Upon the identi
fi
cation of the GW signal GW170817,
preliminary information on this event was rapidly shared with
partner observatories
(
Abbott et al.
2017c
)
. In response,
The Astrophysical Journal Letters,
850:L35
(
18pp
)
, 2017 December 1
https:
//
doi.org
/
10.3847
/
2041-8213
/
aa9aed
© 2017. The American Astronomical Society. All rights reserved.
1
IceCube
(
Bartos et al.
2017a
,
2017b
,
2017c
)
,A
NTARES
(
Ageron et al.
2017a
,
2017b
)
, and Auger
(
Alvarez-Muniz
et al.
2017
)
promptly searched for a neutrino counterpart and
shared their initial results with partner observatories. Subse-
quently, the three facilities carried out a more in-depth search
for a neutrino counterpart using the precise localization of the
source.
This Letter is organized as follows. In Section
2
, we present
the neutrino searches carried out by A
NTARES
, IceCube, and
Auger, as well as the results obtained. In Section
3
, we present
constraints on processes in the merger that can lead to neutrino
emission. We summarize our
fi
ndings and conclude in
Section
4
.
2. Searches and Results
Neutrino observatories detect secondary charged particles
produced in neutrino interaction with matter. Surface detectors,
such as Auger, use arrays of widely spaced water-Cherenkov
detectors to observe the air-shower particles created by high-
energy neutrinos. In detectors such as A
NTARES
and IceCube,
three-dimensional arrays of optical modules deployed in water
or ice detect the Cherenkov radiation from secondary charged
particles that travel through the instrumented detector region.
For these detectors, the secondary particles can create two main
event classes: track-like events from charged-current interac-
tions of muon neutrinos and from a minority of tau neutrino
interactions and shower-like events from all other interactions
(
neutral-current interactions and charged-current interactions of
electron and tau neutrinos
)
. While energy deposition in track-
like events can happen over distances of
(
km
)
, shower-like
events are con
fi
ned to much smaller regions.
For all detectors, neutrino signals must be identi
fi
ed on top
of a persistent background of charged particles produced by the
interaction of cosmic-ray particles with the atmosphere above
the detectors. This discrimination is done by considering the
observed direction and energy of the charged particles. Surface
detectors focus on high-energy
(
10
17
eV
)
showers created
close to the detector by neutrinos from near-horizontal
directions. In-ice and in-water detectors can select well-
reconstructed track events from the up-going direction where
the Earth is used as a natural shield for the dominant
background of penetrating muons from cosmic-ray showers.
By requiring the neutrino interaction vertex to be contained
inside the instrumented volume, or requiring its energy to be
suf
fi
ciently high to be incompatible with the down-going muon
background, even neutrino events originating above the
horizon are identi
fi
able. Neutrinos originating from cosmic-
ray interactions in the atmosphere are also observed and
constitute the primary background for up-going and vertex-
contained event selections.
All three observatories, A
NTARES
, IceCube, and Auger,
performed searches for neutrino signals in coincidence with the
binary neutron star merger event GW170817, each using
multiple event selections. Two different time windows were
used for the searches. First, we used a
±
500 s time window
around the merger to search for neutrinos associated with
prompt and extended gamma-ray emission
(
Baret et al.
2011
;
Kimura et al.
2017
)
. Second, we searched for neutrinos over a
longer 14 day time window following the GW detection, to
cover predictions of longer-lived emission processes
(
e.g., Gao
et al.
2013
; Fang & Metzger
2017
)
.
2.1. ANTARES
The A
NTARES
neutrino telescope has been continuously
operating since 2008. Located deep
(
2500 m
)
in the Mediterra-
nean Sea, 40 km from Toulon
(
France
)
, it is a 10 Mt-scale array
of photosensors, detecting neutrinos with energies above
()
100
GeV.
Based on the originally communicated locations of the GW
signal and the GRB detection, high-energy neutrino candidates
were initially searched for in the A
NTARES
online data stream,
relying on a fast algorithm that selects only up-going neutrino
track candidates
(
Adrián-Martínez et al.
2016b
)
. No up-going
muon neutrino candidate events were found in a
±
500 s time
window centered on the GW event time
—
for an expected
number of atmospheric background events of
∼
10
−
2
during the
coincident time window. An extended online search during
±
1 hr also resulted in no up-going neutrino coincidences.
As it subsequently became clear, the precise direction of
origin of GW170817 in NGC 4993 was above the A
NTARES
horizon at the detection time of the binary merger
(
see
Figure
1
)
. Thus, a dedicated analysis looking for down-going
muon neutrino candidates in the online A
NTARES
data stream
was also performed. No neutrino counterparts were found in
this analysis. The results of these low-latency searches were
shared with follow-up partners within a few hours for the up-
going search and a few days for the down-going search
(
Ageron et al.
2017a
,
2017b
)
.
Here, A
NTARES
used an updated high-energy neutrino
follow-up of GW170817 that includes the shower channel. It
was performed with the of
fl
ine-reconstructed data set that
incorporates dedicated calibration in terms of positioning,
timing, and ef
fi
ciency
(
Aguilar et al.
2011
,
2007
; Adrián-
Martínez et al.
2012
)
. The analysis has been optimized to
increase the sensitivity of the detector and extended to the
longer time window of 14 days.
The search for down-going neutrino counterparts to
GW170817 was made feasible as the large background
affecting this data set can be drastically suppressed by requiring
a time and space coincidence with the GW signal. It was
optimized, independently for tracks and showers, such that a
directional coincidence with NGC 4993 within the search time
window of
±
500 s would have 3
σ
signi
fi
cance. Muon neutrino
candidates were selected by applying cuts on the estimated
angular error and the track quality reconstruction parameter.
While A
NTARES
is sensitive to neutrino events with energy
as small as
()
100 GeV
, the energy range corresponding to
the 5%
–
95% quantiles of the neutrino
fl
ux for an E
−
2
signal
spectrum is equal to
[
32 TeV; 22 PeV
]
. For such a
fl
ux, the
median angular uncertainty, de
fi
ned as the median value of
the distribution of angles between the reconstructed direction of
the event and the true neutrino direction, is equal to 0
°
.5.
Shower events were selected by applying a set of cuts
primarily devoted to reducing the background rate
(
Albert
et al.
2017b
)
. The energy range corresponding to the 5%
–
95%
quantiles of the neutrino
fl
ux for an
-
E
2
signal spectrum is
equal to
[
23 TeV; 16 PeV
]
, while the median angular error is 6
°
with this set of relaxed cuts.
No events temporally coincident with GW170817 were
found. Five background track events
(
likely atmospheric
muons
)
, not compatible with the source position, were detected
(
see Figure
1
)
. We used this non-detection to constrain the
neutrino
fl
uence
(
see Figure
2
)
that was computed as in Adrián-
Martínez et al.
(
2016a
)
.
2
The Astrophysical Journal Letters,
850:L35
(
18pp
)
, 2017 December 1
Albert et al.