of 13
Search for Subsolar Mass Ultracompact Binaries
in Advanced LIGO
s Second Observing Run
B. P. Abbott
etal.
*
(LIGO Scientific Collaboration and the Virgo Collaboration)
(Received 25 May 2019; published 18 October 2019)
We present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO
s
second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run,
this search includes the effects of component spin on the gravitational waveform. We identify no viable
gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one
component between
0
.
2
M
1
.
0
M
. We use the null result to constrain the binary merger rate of (
0
.
2
M
,
0
.
2
M
) binaries to be less than
3
.
7
×
10
5
Gpc
3
yr
1
and the binary merger rate of (
1
.
0
M
,
1
.
0
M
)
binaries to be less than
5
.
2
×
10
3
Gpc
3
yr
1
. Subsolar mass ultracompact objects are not expected to form
via known stellar evolution channels, though it has been suggested that primordial density fluctuations or
particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with
subsolar masses. Assuming a particular primordial black hole (PBH) formation model, we constrain a
population of merging
0
.
2
M
black holes to account for less than 16% of the dark matter density and a
population of merging
1
.
0
M
black holes to account for less than 2% of the dark matter density. We
discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole
population models that predict subsolar mass binaries.
DOI:
10.1103/PhysRevLett.123.161102
Introduction.
Gravitational-wave and multimessenger
astronomy progressed remarkably in Advanced LIGO
[1]
and Advanced Virgo
s
[2]
second observing run, which
included the first observation of gravitational waves from a
binary neutron star merger
[3]
and seven of the ten
observed binary black hole mergers
[4
7]
. These detec-
tions, as well as the candidates presented in the gravita-
tional-wave transient catalog
[7]
, have led to a better
understanding of the populations of compact binaries
detectable by ground based interferometers
[8]
. These
observations, however, represent just a portion of the
parameter space that Advanced LIGO and Advanced
Virgo currently search
[9,10]
and are sensitive to
[11]
.
We report on an extension of the searched parameter space
in data obtained during O2 to compact binaries with
component masses
<
1
M
. To distinguish between other
astrophysical compact objects (e.g., white dwarfs) that are
not compact enough to form binaries that merge within
LIGO
s sensitive frequency band, we label our target
population as
ultracompact
. This is the second search
for subsolar mass ultracompact objects in Advanced
LIGO data and the fourth since initial LIGO
[12
14]
,as
well as the first search to incorporate spin effects into the
modeling of the gravitational-wave emission.
There is no widely accepted mechanism for the for-
mation of ultracompact objects with masses well below a
solar mass within the standard model of particle physics
and the standard
Λ
cold dark matter (
Λ
CDM) model of
cosmology. Neutron stars are expected to have masses
greater than the minimum Chandrasekhar mass
[15]
minus
the gravitational binding energy. Calculations in Ref.
[16]
and more recently in Ref.
[17]
found the minimum mass of
a neutron star to be
1
.
15
M
and
1
.
17
M
, respectively.
These predictions closely agree with the lowest currently
measured neutron star mass of
1
.
17
M
[18]
. Similarly,
black holes formed via established astrophysical collapse
mechanisms are not expected to have masses below the
maximum mass of a nonrotating neutron star, which recent
pulsar timing observations
[19]
suggest is
2
M
. We note
that there is one model that predicts that rapidly rotating
collapsing cores could fission and produce a neutron star
binary
[20,21]
, though this is not a favored astrophysical
mechanism for the production of binary systems.
A detection of a subsolar mass object in a merger would
therefore be a clear signal of new physics. Indeed, there are
several proposals that link subsolar mass compact objects
to proposals for the nature of dark matter, which makes up
nearly 85% of the matter in the Universe. One possibility is
that black holes with masses accessible to ground based
interferometers could have formed deep in the radiation era
from the prompt collapse of large primordial overdensities
on the scale of the early time Hubble volume
[22,23]
. The
size and abundance of any such PBHs depends on the
spectrum of primordial perturbations and on the equation of
*
Full author list given at the end of the article.
PHYSICAL REVIEW LETTERS
123,
161102 (2019)
0031-9007
=
19
=
123(16)
=
161102(13)
161102-1
© 2019 American Physical Society
state of the early Universe
[24
27]
. An alternative infla-
tionary mechanism proposes that vacuum bubbles
nucleated during inflation may result in black holes (with
masses that can be around a solar mass) after inflation
ends
[28]
.
A different class of possibilities, explored more recently,
is motivated by ideas for the particle nature of dark matter.
For example, dark matter may have a sufficiently complex
particle spectrum to support cooling mechanisms that allow
dense regions to collapse into black holes at late times, in
processes analogous to known astrophysical processes
[29]
. Alternatively, dark matter may have interactions with
nuclear matter that allow it to collect inside of neutron stars
and trigger their collapse to black holes
[30
36]
. The
details of when dark matter can collapse a neutron star to
form a black hole or another exotic compact object are still
under investigation
[37]
, but the postulated black holes will
have masses comparable to the progenitor neutron star
mass, or perhaps smaller if some matter can be expelled by
rapid rotation of the star during collapse.
A detection of a subsolar mass black hole would have far-
reaching implications. In the PBH scenario, the mass and
abundance of the black holes would constrain a combination
of the spectrum of initial density perturbations on very small
scales and the equation of state of the Universe at a time
when the typical mass inside a Hubble volume was of the
order of the black hole mass. For particle dark matter
scenarios, the abundance of subsolar mass black holes
would provide a direct estimate of the cooling rate for dark
matter. The black hole mass would constrain the masses of
cosmologically abundant dark matter particles through, for
example, the Chandrasekhar relation for fermions
[29]
or
analogous relations for noninteracting bosons
[38,39]
.In
the case in which all black holes are observed to be near but
not below the mass of neutron stars, the abundance of such
objects would constrain the dark matter-nucleon interaction
strength, as well as the dark matter self-interaction strength
and mass(es)
[36]
.
This Letter reports on the results of a search for
gravitational waves from subsolar mass ultracompact
binaries using data from Advanced LIGO
s second observ-
ing run. No significant candidates consistent with a sub-
solar mass binary were identified. The null result places the
tightest constraints to date on the merger rate and the
abundance of subsolar mass ultracompact binaries. We
describe an extension of our merger rate constraints to
arbitrary populations and models under the assumption that
the horizon distance controls the sensitivity of the search.
We once more consider the merger rate constraints in the
context of merging PBH populations contributing to the
dark matter
[14]
. We describe how to extend the dark matter
fraction parametrization to other models by separating
LIGO observables from model dependent quantities.
Finally, we conclude with a discussion of the implications
of this search.
Search.
We analyze data obtained from November 30,
2016, to August 25, 2017, during Advanced LIGO
s
second observing run (O2)
[40]
. Noise artifacts are linearly
subtracted from the data; this includes strong sinusoidal
features in both detectors due to injected calibration
frequencies and the ac power grid, as well as laser beam
jitter in the LIGO-Hanford detector data
[41]
. We find that
117.53 days of coincident data remain after the application
of data quality cuts
[42
46]
. The Advanced Virgo inter-
ferometer completed commissioning and joined Advanced
LIGO in August 2017 for 15 days of triple coincident
observations
[7]
; however, we report only on the analysis of
data obtained by the LIGO Hanford and LIGO Livingston
interferometers.
The search was conducted using publicly available
gravitational-wave analysis software
[47
53]
. The initial
stage of the search performed a matched-filter analysis using
a discrete bank of template waveforms generated using the
TaylorF2 frequency-domain, post-Newtonian inspiral
approximant. This waveform was chosen since negligible
power is deposited in the merger and ringdown portion of the
waveform for low-mass systems
[54]
. The template bank
used for this search was designed to recover binaries with
component masses of
0
.
19
M
2
.
0
M
and total masses of
0
.
4
M
4
.
0
M
in the detector frame with 97% fidelity, as
in Ref.
[14]
. The search presented here, however, addition-
ally includes spin effects in the modeling of the gravitational
waveform. The bank is constructed to recover gravitational
waves originating from binaries with component spins
purely aligned or antialigned with the orbital angular
momentum, and with dimensionless spin magnitudes of
0.1 or less. The inclusion of spin effects required denser
placement of the waveforms in the template bank; the
resulting bank had 992 461 templates, which is nearly twice
as large as the nonspinning bank used in Ref.
[14]
.
In order to reduce the computational burden, matched
filtering was performed only for a subset of Advanced
LIGO
s full sensitive band
[11]
. The choice to only analyze
the 45
1024 Hz band led to a detector averaged signal-to-
noise ratio (SNR) loss of 8% when compared to the full
10
2048
Hz frequency band. This estimated SNR loss is
a property of Advanced LIGO
s noise curves and is
independent of the templates used in the search; the discrete
nature of the template bank causes an additional
3%
loss
in SNR.
Gravitational-wave candidates that were found coinci-
dent in both the Hanford and Livingston detectors
were ranked using the logarithm of the likelihood ratio,
L
[47
49]
. For a candidate with a likelihood ratio of
L

,we
assign a false-alarm rate (FAR) of
FAR
ð
log
L

Þ¼
N
T
P
ð
log
L
log
L

j
noise
Þ
;
ð
1
Þ
where
N
is the number of observed candidates,
T
is the total
live time of the experiment, and
P
ð
log
L
log
L

j
noise
Þ
PHYSICAL REVIEW LETTERS
123,
161102 (2019)
161102-2
describes the probability that noise produces a candidate
with a ranking statistic at least as high as the candidate
s.
The search recovered the previously detected signal
GW170817
[3]
, which was observed along with an
electromagnetic counterpart
[55]
. This signal is consistent
with a binary neutron star. No other viable gravitational-
wave candidates were identified. The next loudest candi-
date was identified by a template waveform with a chirp
mass of
0
.
23
M
and a SNR of 9.5. The candidate was
consistent with noise and assigned a FAR of 3.25 per year.
Constraint on binary merger rate.
As in Ref.
[14]
,we
consider nine populations of equal mass, nonspinning
binaries that are
δ
-function distributed in mass, i.e.,
m
i
f
0
.
2
;
0
.
3
;
...
;
1
.
0
g
. We injected 913931 fake signals
into our data; the injections were randomly oriented and
spaced uniformly in distance and isotropically across the
sky. The recovered signals provide an estimate of the
pipeline
s detection efficiency as a function of source
distance for each equal mass population. This in turn
allows us to estimate the sensitive volume-time accumu-
lated for each mass bin. We once more use the loudest event
statistic formalism
[56]
to estimate the upper limit on the
binary merger rate to 90% confidence,
R
i
¼
2
.
3
h
VT
i
i
:
ð
2
Þ
These upper limits are shown for equal mass binaries and as
a function of chirp mass in Fig.
1
. Although our template
bank includes systems with a total mass of up to
4
M
,
we place bounds on the merger rate of systems only where
both components are
1
M
. We estimate that detector
calibration uncertainties
[7,57,58]
and Monte Carlo errors
lead to an uncertainty in our rate constraint of no more
than 20%.
Advanced LIGO and Virgo
s horizon distance scales as
D
horizon
M
5
=
6
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Z
f
max
f
min
f
7
=
3
S
n
ð
f
Þ
df
s
;
ð
3
Þ
where
S
n
ð
f
Þ
is the noise spectra of the detector and
f
min
and
f
max
are 45 and 1024 Hz, respectively
[59]
. For a null
result, we therefore expect
R
ð
M
Þ
M
15
=
6
provided that
the horizon distance controls the sensitivity of the search.
The observed power law dependence of the rate constraint
on the chirp mass is within
4%
of the expected
M
15
=
6
dependence; this is well within the error bound on the rate
upper limit and is strong evidence that the chirp mass is the
primary parameter that dictates the sensitivity of the search.
Therefore our upper limits from equal mass systems also
apply to unequal mass systems within the range of mass
ratios we have searched over. For verification, we per-
formed a small injection campaign over five days of
coincident data with injected component masses distributed
between
0
.
19
M
and
2
.
0
M
with at least one component
<
1
.
0
M
. The search sensitivity remained a function of the
chirp mass; this implies that the rate constraints found from
the equal mass injection sets can therefore be applied to
systems with arbitrary mass ratios provided that both
component masses lie within
0
.
20
M
and
1
.
0
M
, where
our injection sets were performed.
The Advanced LIGO and Virgo rate upper limit can be
expanded as
R
ð
M
1
;
M
2
Þ¼
Z
M
2
M
1
R
ð
M
Þ
×
ψ
ð
M
Þ
d
M
;
ð
4
Þ
where
R
is the rate density as a function of chirp mass and
ψ
ð
M
Þ
denotes the black hole population distribution in
chirp mass. We ignore the effects of redshift due to the
small detector range for subsolar mass binaries. Setting
ψ
ð
M
Þ¼
δ
ð
M
Þ
then reveals the form of the LIGO con-
straining rate density,
R
ð
M
Þ
, which is shown in Fig.
1
.For
a given model,
ψ
ð
M
Þ
,
R
ð
M
1
;
M
2
Þ
provides the LIGO
rate constraint on that model for chirp masses between
M
1
and
M
2
. The resulting rate constraints allow direct com-
parison of subsolar mass ultracompact object models with
LIGO observations.
General constraints on subsolar mass black hole dark
matter.
We convert our limits on the merger rate of
subsolar mass ultracompact objects into a constraint on
the abundance of PBHs using our fiducial formation model
[60]
first developed in Refs.
[23,61]
and used previously in
FIG. 1. The constraint on the merger rate density for equal mass
binaries as a function of total mass (top) and chirp mass (bottom).
The two sets of lines show the constraints for the O1 search
[14]
and the O2 search presented here. The null result from O2 places
bounds that are
3
times tighter than the O1 results. The majority
of this improvement is due to the increased coincident observing
time in Advanced LIGO
s second observing run (
118
days vs
48
days), though the improved sensitivity of the detectors led to
an observed physical volume up to
50%
larger than in O1 for
subsolar mass ultracompact binaries.
PHYSICAL REVIEW LETTERS
123,
161102 (2019)
161102-3
LIGO analyses
[12,14]
. We consider a population of equal
mass PBHs that is created deep in the radiation era. We
model the binary formation via three-body interactions,
though others have considered the full field of tidal
interactions
[62]
. By equating the model
s predicted merger
rate with the merger rate upper limit provided by Advanced
LIGO and Virgo, we can numerically solve for the upper
limit on the PBH abundance. These constraints are shown
in Fig.
2 [63]
.
This interpretation is highly model dependent; the mass
distribution, binary fraction, and binary formation mech-
anisms all have a large effect on the expected present day
merger rate and consequently the bounds on the PBH
composition of the dark matter. The Advanced LIGO and
Virgo observables can be separated from the model
dependent terms:
f
CO
¼
ρ
lim
ρ
CDM
×
1
f
obs
¼
R
ð
M
tot
Þ
T
obs
M
tot
ρ
CDM
×
1
f
obs
;
ð
5
Þ
where
T
obs
is the duration of the observation (in the analysis
presented here, 117.53 days). Here we use
f
CO
to refer to
the dark matter fraction in ultracompact objects instead of
f
PBH
to emphasize that this is generally applicable to other
compact object models that could contribute to the dark
matter
[29]
, and not just PBHs. The first term,
ρ
lim
=
ρ
CDM
,
represents the upper limit on the fraction of the dark matter
contained in presently merging subsolar mass ultracompact
binaries. In the second term,
f
obs
describes the fraction of
subsolar mass ultracompact objects that are observable by
Advanced LIGO and Virgo for a particular model. This is
set by the binary fraction and the probability density of
binaries merging at present day. Note that the merger rate
density must be converted from a function of chirp mass to
total mass; this can be done by mapping to total mass for
each mass ratio on an equal chirp mass curve.
Equation
(5)
applies to any dark matter model that
predicts the formation of dark compact objects. The abun-
dance of those dark compact objects can then be expressed
as a fraction of the dark matter density.
Conclusion.
We presented the second Advanced LIGO
and Advanced Virgo search for subsolar mass ultracompact
objects. No unambiguous subsolar mass gravitational-wave
candidates were identified. The null result allowed us to
place tight constraints on the abundance of subsolar mass
ultracompact binaries.
This work represents an expansion of previous initial
and Advanced LIGO and Advanced Virgo subsolar mass
searches. First, we broadened the searched parameter space
to increase sensitivity to systems with non-negligible
component spins. Second, we presented a method to extend
our constraints on the binary merger rate to arbitrarily
distributed populations that contain subsolar mass ultra-
compact objects. Combined with the existing rate limits,
this may already be enough to begin constraining collapsed
particulate dark matter models
[29]
or the cross section of
nuclear interactions
[30
34,36]
. Finally, we provided a
method to separate Advanced LIGO and Advanced Virgo
observables from model dependent terms in our interpre-
tation of the limits on PBH dark matter.
Ground based interferometer searches for subsolar mass
ultracompact objects will continue to inform cosmological
and particle physics scenarios. Advanced LIGO and
Advanced Virgo began a yearlong observing run in early
2019, with improved sensitivities
[70]
.AdvancedVirgowill
have more coincident time with the Advanced LIGO detec-
tors over its next observing run, which will improve network
sensitivity and aid in further constraining theabove scenarios.
The authors gratefully acknowledge the support of the
U.S. National Science Foundation (NSF) for the construc-
tion and operation of the LIGO Laboratory and Advanced
LIGO as well as the Science and Technology Facilities
Council (STFC) of the United Kingdom, the Max Planck
Society (MPS), and the State of Niedersachsen (Germany)
for support of the construction of Advanced LIGO and
FIG. 2. Constraints on the fraction of dark matter comprising
δ
-function distributions of PBHs (
f
PBH
¼
ρ
PBH
=
ρ
DM
). Shown
here are (pink lines) Advanced LIGO constraints from the O1
(dashed lines) and O2 ultracompact binary search presented here
(solid lines), (orange lines) microlensing constraints provided by
the OGLE (solid line), EROS (dashed line)
[64]
, and MACHO
(dotted line) collaborations
[65]
, (cyan lines) dynamical con-
straints from observations of Segue I (solid line)
[66]
and
Eridanus II (dashed line)
[67]
dwarf galaxies, and (blue) super-
nova lensing constraints from the Joint Light-curve Analysis
(solid) and Union 2.1 (dashed) datasets
[68]
. There is an inherent
population model dependency in each of these constraints.
Advanced LIGO and Advanced Virgo results carry an additional
dependence on the binary fraction of the black hole population.
Advanced LIGO and Advanced Virgo results use the Planck
TT,TE,EE+lowP+lensing+ext
cosmology
[69]
.
PHYSICAL REVIEW LETTERS
123,
161102 (2019)
161102-4
construction and operation of the GEO600 detector.
Additional support for Advanced LIGO was provided by
the Australian Research Council. The authors gratefully
acknowledge the Italian Istituto Nazionale di Fisica
Nucleare (INFN), the French Centre National de la
Recherche Scientifique (CNRS), and the Foundation for
Fundamental Research on Matter supported by the
Netherlands Organisation for Scientific Research, for
the construction and operation of the Virgo detector and
the creation and support of the EGO consortium. The
authors also gratefully acknowledge research support from
these agencies as well as by the Council of Scientific and
Industrial Research of India, the Department of Science and
Technology, India, the Science and Engineering Research
Board (SERB), India, the Ministry of Human Resource
Development, India, the Spanish Agencia Estatal
de Investigación, the Vicepresid`
encia i Conselleria
d
Innovació, Recerca i Turisme, and the Conselleria
d
Educació i Universitat del Govern de les Illes Balears,
the Conselleria d
Educació, Investigació, Cultura i Esport
de la Generalitat Valenciana, the National Science Centre
of Poland, the Swiss National Science Foundation
(SNSF), the Russian Foundation for Basic Research, the
Russian Science Foundation, the European Commission,
the European Regional Development Funds (ERDF), the
Royal Society, the Scottish Funding Council, the Scottish
Universities Physics Alliance, the Hungarian Scientific
Research Fund (OTKA), the Lyon Institute of Origins
(LIO), the Paris Île-de-France Region, the National
Research, Development and Innovation Office Hungary
(NKFI), the National Research Foundation of Korea,
Industry Canada and the Province of Ontario through
the Ministry of Economic Development and Innovation,
the Natural Science and Engineering Research Council
Canada, the Canadian Institute for Advanced Research, the
Brazilian Ministry of Science, Technology, Innovations,
and Communications, the International Center for
Theoretical Physics South American Institute for
Fundamental Research (ICTP-SAIFR), the Research
Grants Council of Hong Kong, the National Natural
Science Foundation of China (NSFC), the Leverhulme
Trust, the Research Corporation, the Ministry of Science
and Technology (MOST), Taiwan, and the Kavli
Foundation.Theauthorsgratefully acknowledgethe support
of the NSF, STFC, MPS, INFN, CNRS, and the State of
Niedersachsen (Germany) for provision of computational
resources. Computing resources and personnel for this
project were providedby The Pennsylvania State University.
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37
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1
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29
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3
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66
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24
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7
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16,17
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11
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73
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46
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63,64
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65
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9,10
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1
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1
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14
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74
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75,37
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76,77
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34
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26
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51
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9,10
L. Cadonati,
78
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20,21
J. Casanueva Diaz,
21
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85,32
S. Caudill,
37
M. Cavagli`
a,
86,87
F. Cavalier,
28
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29
G. Cella,
21
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J. George,
60
L. Gergely,
132
S. Ghonge,
78
Abhirup Ghosh,
76
Archisman Ghosh,
37
S. Ghosh,
24
B. Giacomazzo,
118,119
J. A. Giaime,
2,7
K. D. Giardina,
7
D. R. Gibson,
133
K. Gill,
106
L. Glover,
134
J. Gniesmer,
135
P. Godwin,
89
E. Goetz,
47
R. Goetz,
30
B. Goncharov,
6
G. González,
2
J. M. Gonzalez Castro,
20,21
A. Gopakumar,
136
S. E. Gossan,
1
M. Gosselin,
29,20,21
R. Gouaty,
34
B. Grace,
8
A. Grado,
137,5
M. Granata,
23
A. Grant,
46
S. Gras,
14
P. Grassia,
1
C. Gray,
47
R. Gray,
46
G. Greco,
63,64
A. C. Green,
30
R. Green,
107
E. M. Gretarsson,
35
A. Grimaldi,
118,119
S. J. Grimm,
16,17
P. Groot,
67
H. Grote,
107
S. Grunewald,
76
P. Gruning,
28
G. M. Guidi,
63,64
H. K. Gulati,
112
Y. Guo,
37
A. Gupta,
89
Anchal Gupta,
1
P. Gupta,
37
E. K. Gustafson,
1
R. Gustafson,
138
L. Haegel,
102
O. Halim,
17,16
B. R. Hall,
139
E. D. Hall,
14
E. Z. Hamilton,
107
G. Hammond,
46
M. Haney,
70
M. M. Hanke,
9,10
J. Hanks,
47
C. Hanna,
89
M. D. Hannam,
107
O. A. Hannuksela,
94
T. J. Hansen,
35
J. Hanson,
7
T. Harder,
65
T. Hardwick,
2
K. Haris,
18
J. Harms,
16,17
G. M. Harry,
140
I. W. Harry,
141
R. K. Hasskew,
7
C. J. Haster,
14
K. Haughian,
46
F. J. Hayes,
46
J. Healy,
62
A. Heidmann,
73
M. C. Heintze,
7
H. Heitmann,
65
F. Hellman,
142
P. Hello,
28
G. Hemming,
29
M. Hendry,
46
I. S. Heng,
46
J. Hennig,
9,10
M. Heurs,
9,10
S. Hild,
46
T. Hinderer,
143,37,144
S. Hochheim,
9,10
D. Hofman,
23
A. M. Holgado,
19
N. A. Holland,
8
K. Holt,
7
D. E. Holz,
93
P. Hopkins,
107
C. Horst,
24
J. Hough,
46
E. J. Howell,
66
C. G. Hoy,
107
Y. Huang,
14
M. T. Hübner,
6
E. A. Huerta,
19
D. Huet,
28
B. Hughey,
35
V. Hui,
34
S. Husa,
102
S. H. Huttner,
46
T. Huynh-Dinh,
7
B. Idzkowski,
74
A. Iess,
85,32
H. Inchauspe,
30
C. Ingram,
57
R. Inta,
84
G. Intini,
120,33
B. Irwin,
122
H. N. Isa,
46
J.-M. Isac,
73
M. Isi,
14
B. R. Iyer,
18
T. Jacqmin,
73
S. J. Jadhav,
145
K. Jani,
78
N. N. Janthalur,
145
P. Jaranowski,
146
D. Jariwala,
30
A. C. Jenkins,
147
J. Jiang,
30
D. S. Johnson,
19
A. W. Jones,
13
D. I. Jones,
148
J. D. Jones,
47
R. Jones,
46
R. J. G. Jonker,
37
L. Ju,
66
J. Junker,
9,10
C. V. Kalaghatgi,
107
V. Kalogera,
58
B. Kamai,
1
S. Kandhasamy,
3
G. Kang,
38
J. B. Kanner,
1
S. J. Kapadia,
24
S. Karki,
72
R. Kashyap,
18
M. Kasprzack,
1
S. Katsanevas,
29
E. Katsavounidis,
14
W. Katzman,
7
S. Kaufer,
10
K. Kawabe,
47
N. V. Keerthana,
3
F. K ́
ef ́
elian,
65
D. Keitel,
141
R. Kennedy,
113
J. S. Key,
149
F. Y. Khalili,
61
I. Khan,
16,32
S. Khan,
9,10
E. A. Khazanov,
150
N. Khetan,
16,17
M. Khursheed,
60
N. Kijbunchoo,
8
Chunglee Kim,
151
J. C. Kim,
152
K. Kim,
94
W. Kim,
57
W. S. Kim,
153
Y.-M. Kim,
154
C. Kimball,
58
P. J. King,
47
M. Kinley-Hanlon,
46
R. Kirchhoff,
9,10
J. S. Kissel,
47
L. Kleybolte,
135
J. H. Klika,
24
S. Klimenko,
30
T. D. Knowles,
39
P. Koch,
9,10
S. M. Koehlenbeck,
9,10
G. Koekoek,
37,155
S. Koley,
37
V. Kondrashov,
1
A. Kontos,
156
N. Koper,
9,10
M. Korobko,
135
W. Z. Korth,
1
M. Kovalam,
66
D. B. Kozak,
1
C. Krämer,
9,10
V. Kringel,
9,10
N. Krishnendu,
31
A. Królak,
157,158
N. Krupinski,
24
G. Kuehn,
9,10
A. Kumar,
145
P. Kumar,
159
Rahul Kumar,
47
Rakesh Kumar,
112
L. Kuo,
90
A. Kutynia,
157
S. Kwang,
24
B. D. Lackey,
76
D. Laghi,
20,21
K. H. Lai,
94
T. L. Lam,
94
M. Landry,
47
B. B. Lane,
14
R. N. Lang,
160
J. Lange,
62
B. Lantz,
51
R. K. Lanza,
14
A. Lartaux-Vollard,
28
P. D. Lasky,
6
M. Laxen,
7
A. Lazzarini,
1
C. Lazzaro,
54
P. Leaci,
120,33
S. Leavey,
9,10
Y. K. Lecoeuche,
47
C. H. Lee,
97
H. K. Lee,
161
H. M. Lee,
162
H. W. Lee,
152
J. Lee,
96
K. Lee,
46
J. Lehmann,
9,10
A. K. Lenon,
39
N. Leroy,
28
N. Letendre,
34
Y. Levin,
6
A. Li,
94
J. Li,
83
K. J. L. Li,
94
T. G. F. Li,
94
X. Li,
48
F. Lin,
6
F. Linde,
163,37
S. D. Linker,
134
T. B. Littenberg,
164
J. Liu,
66
X. Liu,
24
M. Llorens-Monteagudo,
22
R. K. L. Lo,
94,1
L. T. London,
14
A. Longo,
165,166
M. Lorenzini,
16,17
V. Loriette,
167
M. Lormand,
7
G. Losurdo,
21
J. D. Lough,
9,10
C. O. Lousto,
62
G. Lovelace,
27
M. E. Lower,
168
H. Lück,
10,9
D. Lumaca,
85,32
A. P. Lundgren,
141
R. Lynch,
14
Y. Ma,
48
R. Macas,
107
PHYSICAL REVIEW LETTERS
123,
161102 (2019)
161102-8
S. Macfoy,
25
M. MacInnis,
14
D. M. Macleod,
107
A. Macquet,
65
I. Magaña Hernandez,
24
F. Magaña-Sandoval,
30
R. M. Magee,
89
E. Majorana,
33
I. Maksimovic,
167
A. Malik,
60
N. Man,
65
V. Mandic,
43
V. Mangano,
46,120,33
G. L. Mansell,
47,14
M. Manske,
24
M. Mantovani,
29
M. Mapelli,
53,54
F. Marchesoni,
52,41
F. Marion,
34
S. Márka,
106
Z. Márka,
106
C. Markakis,
19
A. S. Markosyan,
51
A. Markowitz,
1
E. Maros,
1
A. Marquina,
105
S. Marsat,
26
F. Martelli,
63,64
I. W. Martin,
46
R. M. Martin,
36
V. Martinez,
79
D. V. Martynov,
13
H. Masalehdan,
135
K. Mason,
14
E. Massera,
113
A. Masserot,
34
T. J. Massinger,
1
M. Masso-Reid,
46
S. Mastrogiovanni,
26
A. Matas,
76
F. Matichard,
1,14
L. Matone,
106
N. Mavalvala,
14
J. J. McCann,
66
R. McCarthy,
47
D. E. McClelland,
8
P. McClincy,
89
S. McCormick,
7
L. McCuller,
14
S. C. McGuire,
169
C. McIsaac,
141
J. McIver,
1
D. J. McManus,
8
T. McRae,
8
S. T. McWilliams,
39
D. Meacher,
24
G. D. Meadors,
6
M. Mehmet,
9,10
A. K. Mehta,
18
J. Meidam,
37
E. Mejuto Villa,
117,69
A. Melatos,
101
G. Mendell,
47
R. A. Mercer,
24
L. Mereni,
23
K. Merfeld,
72
E. L. Merilh,
47
M. Merzougui,
65
S. Meshkov,
1
C. Messenger,
46
C. Messick,
89
F. Messina,
44,45
R. Metzdorff,
73
P. M. Meyers,
101
F. Meylahn,
9,10
A. Miani,
118,119
H. Miao,
13
C. Michel,
23
H. Middleton,
101
L. Milano,
80,5
A. L. Miller,
30,120,33
M. Millhouse,
101
J. C. Mills,
107
M. C. Milovich-Goff,
134
O. Minazzoli,
65,170
Y. Minenkov,
32
A. Mishkin,
30
C. Mishra,
171
T. Mistry,
113
S. Mitra,
3
V. P. Mitrofanov,
61
G. Mitselmakher,
30
R. Mittleman,
14
G. Mo,
98
D. Moffa,
122
K. Mogushi,
86
S. R. P. Mohapatra,
14
M. Molina-Ruiz,
142
M. Mondin,
134
M. Montani,
63,64
C. J. Moore,
13
D. Moraru,
47
F. Morawski,
56
G. Moreno,
47
S. Morisaki,
82
B. Mours,
34
C. M. Mow-Lowry,
13
F. Muciaccia,
120,33
Arunava Mukherjee,
9,10
D. Mukherjee,
24
S. Mukherjee,
109
Subroto Mukherjee,
112
N. Mukund,
9,10,3
A. Mullavey,
7
J. Munch,
57
E. A. Muñiz,
42
M. Muratore,
35
P. G. Murray,
46,128,172
I. Nardecchia,
85,32
L. Naticchioni,
120,33
R. K. Nayak,
173
B. F. Neil,
66
J. Neilson,
117,69
G. Nelemans,
67,37
T. J. N. Nelson,
7
M. Nery,
9,10
A. Neunzert,
138
L. Nevin,
1
K. Y. Ng,
14
S. Ng,
57
C. Nguyen,
26
P. Nguyen,
72
D. Nichols,
143,37
S. A. Nichols,
2
S. Nissanke,
143,37
F. Nocera,
29
C. North,
107
L. K. Nuttall,
141
M. Obergaulinger,
22,174
J. Oberling,
47
B. D. O
Brien,
30
G. Oganesyan,
16,17
G. H. Ogin,
175
J. J. Oh,
153
S. H. Oh,
153
F. Ohme,
9,10
H. Ohta,
82
M. A. Okada,
15
M. Oliver,
102
P. Oppermann,
9,10
Richard J. Oram,
7
B. O
Reilly,
7
R. G. Ormiston,
43
L. F. Ortega,
30
R. O
Shaughnessy,
62
S. Ossokine,
76
D. J. Ottaway,
57
H. Overmier,
7
B. J. Owen,
84
A. E. Pace,
89
G. Pagano,
20,21
M. A. Page,
66
G. Pagliaroli,
16,17
A. Pai,
131
S. A. Pai,
60
J. R. Palamos,
72
O. Palashov,
150
C. Palomba,
33
H. Pan,
90
P. K. Panda,
145
P. T. H. Pang,
94,37
C. Pankow,
58
F. Pannarale,
120,33
B. C. Pant,
60
F. Paoletti,
21
A. Paoli,
29
A. Parida,
3
W. Parker,
7,169
D. Pascucci,
46,37
A. Pasqualetti,
29
R. Passaquieti,
20,21
D. Passuello,
21
M. Patil,
158
B. Patricelli,
20,21
E. Payne,
6
B. L. Pearlstone,
46
T. C. Pechsiri,
30
A. J. Pedersen,
42
M. Pedraza,
1
R. Pedurand,
23,176
A. Pele,
7
S. Penn,
177
A. Perego,
118,119
C. J. Perez,
47
C. P ́
erigois,
34
A. Perreca,
118,119
J. Petermann,
135
H. P. Pfeiffer,
76
M. Phelps,
9,10
K. S. Phukon,
3
O. J. Piccinni,
120,33
M. Pichot,
65
F. Piergiovanni,
63,64
V. Pierro,
117,69
G. Pillant,
29
L. Pinard,
23
I. M. Pinto,
117,69,88
M. Pirello,
47
M. Pitkin,
46
W. Plastino,
165,166
R. Poggiani,
20,21
D. Y. T. Pong,
94
S. Ponrathnam,
3
P. Popolizio,
29
E. K. Porter,
26
J. Powell,
168
A. K. Prajapati,
112
J. Prasad,
3
K. Prasai,
51
R. Prasanna,
145
G. Pratten,
102
T. Prestegard,
24
M. Principe,
117,88,69
G. A. Prodi,
118,119
L. Prokhorov,
13
M. Punturo,
41
P. Puppo,
33
M. Pürrer,
76
H. Qi,
107
V. Quetschke,
109
P. J. Quinonez,
35
F. J. Raab,
47
G. Raaijmakers,
143,37
H. Radkins,
47
N. Radulesco,
65
P. Raffai,
111
S. Raja,
60
C. Rajan,
60
B. Rajbhandari,
84
M. Rakhmanov,
109
K. E. Ramirez,
109
A. Ramos-Buades,
102
Javed Rana,
3
K. Rao,
58
P. Rapagnani,
120,33
V. Raymond,
107
M. Razzano,
20,21
J. Read,
27
T. Regimbau,
34
L. Rei,
59
S. Reid,
25
D. H. Reitze,
1,30
P. Rettegno,
128,178
F. Ricci,
120,33
C. J. Richardson,
35
J. W. Richardson,
1
P. M. Ricker,
19
G. Riemenschneider,
178,128
K. Riles,
138
M. Rizzo,
58
N. A. Robertson,
1,46
F. Robinet,
28
A. Rocchi,
32
L. Rolland,
34
J. G. Rollins,
1
V. J. Roma,
72
M. Romanelli,
71
R. Romano,
4,5
C. L. Romel,
47
J. H. Romie,
7
C. A. Rose,
24
D. Rose,
27
K. Rose,
122
D. Rosi
ń
ska,
74
S. G. Rosofsky,
19
M. P. Ross,
179
S. Rowan,
46
A. Rüdiger,
9,10
,a
P. Ruggi,
29
G. Rutins,
133
K. Ryan,
47
S. Sachdev,
89
T. Sadecki,
47
M. Sakellariadou,
147
O. S. Salafia,
180,44,45
L. Salconi,
29
M. Saleem,
31
A. Samajdar,
37
L. Sammut,
6
E. J. Sanchez,
1
L. E. Sanchez,
1
N. Sanchis-Gual,
181
J. R. Sanders,
182
K. A. Santiago,
36
E. Santos,
65
N. Sarin,
6
B. Sassolas,
23
B. S. Sathyaprakash,
89,107
O. Sauter,
138,34
R. L. Savage,
47
P. Schale,
72
M. Scheel,
48
J. Scheuer,
58
P. Schmidt,
13,67
R. Schnabel,
135
R. M. S. Schofield,
72
A. Schönbeck,
135
E. Schreiber,
9,10
B. W. Schulte,
9,10
B. F. Schutz,
107
J. Scott,
46
S. M. Scott,
8
E. Seidel,
19
D. Sellers,
7
A. S. Sengupta,
183
N. Sennett,
76
D. Sentenac,
29
V. Sequino,
59
A. Sergeev,
150
Y. Setyawati,
9,10
D. A. Shaddock,
8
T. Shaffer,
47
M. S. Shahriar,
58
M. B. Shaner,
134
A. Sharma,
16,17
P. Sharma,
60
P. Shawhan,
77
H. Shen,
19
R. Shink,
184
D. H. Shoemaker,
14
D. M. Shoemaker,
78
K. Shukla,
142
S. ShyamSundar,
60
K. Siellez,
78
M. Sieniawska,
56
D. Sigg,
47
L. P. Singer,
81
D. Singh,
89
N. Singh,
74
A. Singhal,
16,33
A. M. Sintes,
102
S. Sitmukhambetov,
109
V. Skliris,
107
B. J. J. Slagmolen,
8
T. J. Slaven-Blair,
66
J. R. Smith,
27
R. J. E. Smith,
6
S. Somala,
185
E. J. Son,
153
S. Soni,
2
B. Sorazu,
46
F. Sorrentino,
59
T. Souradeep,
3
E. Sowell,
84
A. P. Spencer,
46
M. Spera,
53,54
A. K. Srivastava,
112
V. Srivastava,
42
K. Staats,
58
C. Stachie,
65
M. Standke,
9,10
D. A. Steer,
26
M. Steinke,
9,10
PHYSICAL REVIEW LETTERS
123,
161102 (2019)
161102-9
J. Steinlechner,
135,46
S. Steinlechner,
135
D. Steinmeyer,
9,10
S. P. Stevenson,
168
D. Stocks,
51
R. Stone,
109
D. J. Stops,
13
K. A. Strain,
46
G. Stratta,
186,64
S. E. Strigin,
61
A. Strunk,
47
R. Sturani,
187
A. L. Stuver,
188
V. Sudhir,
14
T. Z. Summerscales,
189
L. Sun,
1
S. Sunil,
112
A. Sur,
56
J. Suresh,
82
P. J. Sutton,
107
B. L. Swinkels,
37
M. J. Szczepa
ń
czyk,
35
M. Tacca,
37
S. C. Tait,
46
C. Talbot,
6
D. B. Tanner,
30
D. Tao,
1
M. Tápai,
132
A. Tapia,
27
J. D. Tasson,
98
R. Taylor,
1
R. Tenorio,
102
L. Terkowski,
135
M. Thomas,
7
P. Thomas,
47
S. R. Thondapu,
60
K. A. Thorne,
7
E. Thrane,
6
Shubhanshu Tiwari,
118,119
Srishti Tiwari,
136
V. Tiwari,
107
K. Toland,
46
M. Tonelli,
20,21
Z. Tornasi,
46
A. Torres-Forn ́
e,
190
C. I. Torrie,
1
D. Töyrä,
13
F. Travasso,
29,41
G. Traylor,
7
M. C. Tringali,
74
A. Tripathee,
138
A. Trovato,
26
L. Trozzo,
191,21
K. W. Tsang,
37
M. Tse,
14
R. Tso,
48
L. Tsukada,
82
D. Tsuna,
82
T. Tsutsui,
82
D. Tuyenbayev,
109
K. Ueno,
82
D. Ugolini,
192
C. S. Unnikrishnan,
136
A. L. Urban,
2
S. A. Usman,
93
H. Vahlbruch,
10
G. Vajente,
1
G. Valdes,
2
M. Valentini,
118,119
N. van Bakel,
37
M. van Beuzekom,
37
J. F. J. van den Brand,
75,37
C. Van Den Broeck,
37,193
D. C. Vander-Hyde,
42
L. van der Schaaf,
37
J. V. VanHeijningen,
66
A. A. van Veggel,
46
M. Vardaro,
53,54
V. Varma,
48
S. Vass,
1
M. Vasúth,
50
A. Vecchio,
13
G. Vedovato,
54
J. Veitch,
46
P. J. Veitch,
57
K. Venkateswara,
179
G. Venugopalan,
1
D. Verkindt,
34
F. Vetrano,
63,64
A. Vicer ́
e,
63,64
A. D. Viets,
24
S. Vinciguerra,
13
D. J. Vine,
133
J.-Y. Vinet,
65
S. Vitale,
14
T. Vo,
42
H. Vocca,
40,41
C. Vorvick,
47
S. P. Vyatchanin,
61
A. R. Wade,
1
L. E. Wade,
122
M. Wade,
122
R. Walet,
37
M. Walker,
27
L. Wallace,
1
S. Walsh,
24
H. Wang,
13
J. Z. Wang,
138
S. Wang,
19
W. H. Wang,
109
Y. F. Wang,
94
R. L. Ward,
8
Z. A. Warden,
35
J. Warner,
47
M. Was,
34
J. Watchi,
103
B. Weaver,
47
L.-W. Wei,
9,10
M. Weinert,
9,10
A. J. Weinstein,
1
R. Weiss,
14
F. Wellmann,
9,10
L. Wen,
66
E. K. Wessel,
19
P. Weßels,
9,10
J. W. Westhouse,
35
K. Wette,
8
J. T. Whelan,
62
B. F. Whiting,
30
C. Whittle,
14
D. M. Wilken,
9,10
D. Williams,
46
A. R. Williamson,
143,37
J. L. Willis,
1
B. Willke,
10,9
W. Winkler,
9,10
C. C. Wipf,
1
H. Wittel,
9,10
G. Woan,
46
J. Woehler,
9,10
J. K. Wofford,
62
J. L. Wright,
46
D. S. Wu,
9,10
D. M. Wysocki,
62
S. Xiao,
1
R. Xu,
110
H. Yamamoto,
1
C. C. Yancey,
77
L. Yang,
121
Y. Yang,
30
Z. Yang,
43
M. J. Yap,
8
M. Yazback,
30
D. W. Yeeles,
107
Hang Yu,
14
Haocun Yu,
14
S. H. R. Yuen,
94
A. K. Zadro
ż
ny,
109
A. Zadro
ż
ny,
157
M. Zanolin,
35
T. Zelenova,
29
J.-P. Zendri,
54
M. Zevin,
58
J. Zhang,
66
L. Zhang,
1
T. Zhang,
46
C. Zhao,
66
G. Zhao,
103
M. Zhou,
58
Z. Zhou,
58
X. J. Zhu,
6
A. B. Zimmerman,
194
M. E. Zucker,
1,14
and J. Zweizig
1
(LIGO Scientific Collaboration and the Virgo Collaboration)
S. Shandera
89
1
LIGO, California Institute of Technology, Pasadena, California 91125, USA
2
Louisiana State University, Baton Rouge, Louisiana 70803, USA
3
Inter-University Centre for Astronomy and Astrophysics, Pune 411007, India
4
Dipartimento di Farmacia, Universit`
a di Salerno, I-84084 Fisciano, Salerno, Italy
5
INFN, Sezione di Napoli, Complesso Universitario di Monte Sant
Angelo, I-80126 Napoli, Italy
6
OzGrav, School of Physics and Astronomy, Monash University, Clayton 3800, Victoria, Australia
7
LIGO Livingston Observatory, Livingston, Louisiana 70754, USA
8
OzGrav, Australian National University, Canberra, Australian Capital Territory 0200, Australia
9
Max Planck Institute for Gravitational Physics (Albert Einstein Institute), D-30167 Hannover, Germany
10
Leibniz Universität Hannover, D-30167 Hannover, Germany
11
Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena, D-07743 Jena, Germany
12
University of Cambridge, Cambridge CB2 1TN, United Kingdom
13
University of Birmingham, Birmingham B15 2TT, United Kingdom
14
LIGO, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
15
Instituto Nacional de Pesquisas Espaciais, 12227-010 São Jos ́
e dos Campos, São Paulo, Brazil
16
Gran Sasso Science Institute (GSSI), I-67100 L
Aquila, Italy
17
INFN, Laboratori Nazionali del Gran Sasso, I-67100 Assergi, Italy
18
International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru 560089, India
19
NCSA, University of Illinois at Urbana
Champaign, Urbana, Illinois 61801, USA
20
Universit`
a di Pisa, I-56127 Pisa, Italy
21
INFN, Sezione di Pisa, I-56127 Pisa, Italy
22
Departamento de Astronomía y Astrofísica, Universitat de Val`
encia, E-46100 Burjassot, Val`
encia, Spain
23
Laboratoire des Mat ́
eriaux Avanc ́
es (LMA), CNRS/IN2P3, F-69622 Villeurbanne, France
24
University of Wisconsin
Milwaukee, Milwaukee, Wisconsin 53201, USA
25
SUPA, University of Strathclyde, Glasgow G1 1XQ, United Kingdom
26
APC, AstroParticule et Cosmologie, Universit ́
e Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cit ́
e,
F-75205 Paris Cedex 13, France
27
California State University Fullerton, Fullerton, California 92831, USA
28
LAL, Universit ́
e Paris
Sud, CNRS/IN2P3, Universit ́
e Paris
Saclay, F-91898 Orsay, France
PHYSICAL REVIEW LETTERS
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29
European Gravitational Observatory (EGO), I-56021 Cascina, Pisa, Italy
30
University of Florida, Gainesville, Florida 32611, USA
31
Chennai Mathematical Institute, Chennai 603103, India
32
INFN, Sezione di Roma Tor Vergata, I-00133 Roma, Italy
33
INFN, Sezione di Roma, I-00185 Roma, Italy
34
Laboratoire d
Annecy de Physique des Particules (LAPP), Universit ́
e Grenoble Alpes, Universit ́
e Savoie Mont Blanc,
CNRS/IN2P3, F-74941 Annecy, France
35
Embry-Riddle Aeronautical University, Prescott, Arizona 86301, USA
36
Montclair State University, Montclair, New Jersey 07043, USA
37
Nikhef, Science Park 105, 1098 XG Amsterdam, Netherlands
38
Korea Institute of Science and Technology Information, Daejeon 34141, Korea
39
West Virginia University, Morgantown, West Virginia 26506, USA
40
Universit`
a di Perugia, I-06123 Perugia, Italy
41
INFN, Sezione di Perugia, I-06123 Perugia, Italy
42
Syracuse University, Syracuse, New York 13244, USA
43
University of Minnesota, Minneapolis, Minnesota 55455, USA
44
Universit`
a degli Studi di Milano-Bicocca, I-20126 Milano, Italy
45
INFN, Sezione di Milano-Bicocca, I-20126 Milano, Italy
46
SUPA, University of Glasgow, Glasgow G12 8QQ, United Kingdom
47
LIGO Hanford Observatory, Richland, Washington 99352, USA
48
Caltech CaRT, Pasadena, California 91125, USA
49
Dipartimento di Medicina, Chirurgia e Odontoiatria
Scuola Medica Salernitana,
Universit`
a di Salerno,
I-84081 Baronissi, Salerno, Italy
50
Wigner RCP, RMKI, H-1121 Budapest, Konkoly Thege Miklós út 29-33, Hungary
51
Stanford University, Stanford, California 94305, USA
52
Universit`
a di Camerino, Dipartimento di Fisica, I-62032 Camerino, Italy
53
Universit`
a di Padova, Dipartimento di Fisica e Astronomia, I-35131 Padova, Italy
54
INFN, Sezione di Padova, I-35131 Padova, Italy
55
Montana State University, Bozeman, Montana 59717, USA
56
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, 00-716 Warsaw, Poland
57
OzGrav, University of Adelaide, Adelaide, South Australia 5005, Australia
58
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University,
Evanston, Illinois 60208, USA
59
INFN, Sezione di Genova, I-16146 Genova, Italy
60
RRCAT, Indore, Madhya Pradesh 452013, India
61
Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
62
Rochester Institute of Technology, Rochester, New York 14623, USA
63
Universit`
a degli Studi di Urbino
Carlo Bo,
I-61029 Urbino, Italy
64
INFN, Sezione di Firenze, I-50019 Sesto Fiorentino, Firenze, Italy
65
Artemis, Universit ́
e Côte d
Azur, Observatoire Côte d
Azur, CNRS, CS 34229, F-06304 Nice Cedex 4, France
66
OzGrav, University of Western Australia, Crawley, Western Australia 6009, Australia
67
Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, Netherlands
68
Dipartimento di Fisica
E.R. Caianiello,
Universit`
a di Salerno, I-84084 Fisciano, Salerno, Italy
69
INFN, Sezione di Napoli, Gruppo Collegato di Salerno, Complesso Universitario di Monte Sant
Angelo, I-80126 Napoli, Italy
70
Physik-Institut, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
71
Universit ́
e Rennes, CNRS, Institut FOTON
UMR6082, F-3500 Rennes, France
72
University of Oregon, Eugene, Oregon 97403, USA
73
Laboratoire Kastler Brossel, Sorbonne Universit ́
e, CNRS, ENS
Universit ́
e PSL, Coll`
ege de France, F-75005 Paris, France
74
Astronomical Observatory Warsaw University, 00-478 Warsaw, Poland
75
VU University Amsterdam, 1081 HV Amsterdam, Netherlands
76
Max Planck Institute for Gravitational Physics (Albert Einstein Institute), D-14476 Potsdam-Golm, Germany
77
University of Maryland, College Park, Maryland 20742, USA
78
School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
79
Universit ́
e de Lyon, Universit ́
e Claude Bernard Lyon 1, CNRS, Institut Lumi`
ere Mati`
ere, F-69622 Villeurbanne, France
80
Universit`
a di Napoli
Federico II,
Complesso Universitario di Monte Sant
Angelo, I-80126 Napoli, Italy
81
NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
82
RESCEU, University of Tokyo, Tokyo 113-0033, Japan
83
Tsinghua University, Beijing 100084, China
84
Texas Tech University, Lubbock, Texas 79409, USA
85
Universit`
a di Roma Tor Vergata, I-00133 Roma, Italy
PHYSICAL REVIEW LETTERS
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