of 54
Living Rev Relativ (2018) 21:3
DOI:10.1007/s41114-018-0012-9
Prospects for Observing and Localizing Gravitational-Wave
Transients with Advanced LIGO, Advanced Virgo and
KAGRA
Abbott, B. P. et al. (KAGRA Collaboration, LIGO
Scientific Collaboration and Virgo Collaboration)
Received: 11 September 2017 / Accepted: 7 February 2018
Abstract
We present possible observing scenarios for the Advanced LIGO, Advanced
Virgo and KAGRA gravitational-wave detectors over the next decade, with the in-
tention of providing information to the astronomy community to facilitate planning
for multi-messenger astronomy with gravitational waves. We estimate the sensitivity
of the network to transient gravitational-wave signals, and study the capability of
the network to determine the sky location of the source. We report our findings for
gravitational-wave transients, with particular focus on gravitational-wave signals from
the inspiral of binary neutron star systems, which are the most promising targets for
multi-messenger astronomy. The ability to localize the sources of the detected signals
depends on the geographical distribution of the detectors and their relative sensitivity,
and
90%
credible regions can be as large as thousands of square degrees when only
two sensitive detectors are operational. Determining the sky position of a significant
fraction of detected signals to areas of
5
20 deg
2
requires at least three detectors of
sensitivity within a factor of
2
of each other and with a broad frequency bandwidth.
When all detectors, including KAGRA and the third LIGO detector in India, reach
design sensitivity, a significant fraction of gravitational-wave signals will be localized
to a few square degrees by gravitational-wave observations alone.
Keywords
Gravitational waves
·
Gravitational-wave detectors
·
Electromagnetic
counterparts
·
Data analysis
PACS
04.30.–w
·
04.80.Nn
·
95.55.Ym
·
95.85.Sz
The full author list and affiliations are given at the end of paper.
arXiv:1304.0670v6 [gr-qc] 26 Apr 2018
2
KAGRA Collaboration, LIGO Scientific Collaboration and Virgo Collaboration
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2 Commissioning and observing phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.1
Commissioning and observing roadmap . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.2
Past and envisioned observing schedule . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
3 Searches for gravitational-wave transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.1
Detection and false alarm rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2
Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4 Observing scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.1
2015 – 2016 run (O1): aLIGO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2
2016 – 2017 run (O2): aLIGO joined by AdV . . . . . . . . . . . . . . . . . . . . . . . . 25
4.3
2018 – 2019 run (O3): aLIGO 120 – 170 Mpc, AdV 65 – 85 Mpc . . . . . . . . . . . . . . 26
4.4
2020+ runs: aLIGO 190 Mpc, AdV 65 – 125 Mpc . . . . . . . . . . . . . . . . . . . . . . 26
4.5
2024+ runs: aLIGO (including LIGO-India) 190 Mpc, AdV 125 Mpc, KAGRA 140 Mpc .
27
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
A Changes between versions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
A.1 Updates to detector commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
A.2 Updates to data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
1 Introduction
Advanced LIGO (aLIGO; Harry 2010; Aasi et al 2015a), Advanced Virgo (AdV;
Acernese et al 2009; Accadia et al 2012; Acernese et al 2015) and KAGRA (Somiya
2012; Aso et al 2013) are kilometer-scale gravitational-wave (
GW
) detectors that
are sensitive to
GW
s with frequencies of
20
2000 Hz
.
1
The era of
GW
astron-
omy began with the detection of GW150914 (Abbott et al 2016k), a signal from
the coalescence of a binary black hole (
BBH
); the first confirmed multi-messenger
counterpart to a
GW
observation came with GW170817 (Abbott et al 2017a), a signal
from a binary neutron star (
BNS
) coalescence which was accompanied by detections
across the electromagnetic spectrum (Abbott et al 2017k). In this article, we describe
the currently projected schedule, sensitivity, and sky-localization accuracy for the
GW
-detector network. We discuss the past and future planned sequence of observing
runs (designated O1, O2, O3, etc.) and the prospects for multi-messenger astronomy.
The purpose of this article is to provide information to the astronomy community
to assist in the formulation of plans for forthcoming
GW
observations. In particular,
we intend this article to provide the information required for assessing the features of
programs for joint observation of
GW
events using electromagnetic, neutrino, or other
facilities (e.g., Abbott et al 2016i; Adrian-Martinez et al 2016; Albert et al 2017c;
Abbott et al 2017k).
The full science of ground-based
GW
detectors is broad (Abbott et al 2016j),
and is not covered in this article. We concentrate solely on candidate
GW
transient
signals. We place particular emphasis on the coalescence of
BNS
systems, which are
the
GW
source for which electromagnetic follow-up is most promising (Metzger and
1
LIGO is short for Laser Interferometer Gravitational-Wave Observatory. KAGRA is named after
the Japanese word for traditional sacred music and dance for the gods
kagura
; the name has a secondary
meaning as an abbreviation for KAmioka GRavitational-wave Antenna. Virgo is not an acronym, and is not
written in all caps.
Prospects for Observing and Localizing GW Transients with aLIGO, AdV and KAGRA
3
Berger 2012; Patricelli et al 2016; Paschalidis 2017; Rosswog et al 2017; Metzger
2017). However, we also mention
BBH
s, as they are the most commonly detected
source (Abbott et al 2016d, 2017g). No electromagnetic emission is expected for
vacuum
BBH
mergers (Centrella et al 2010), but is possible if there is surrounding
material (Schnittman 2013), for example, remnants of mass lost from the parent
star (Perna et al 2016; Janiuk et al 2017) or if the binary was embedded in a circumbi-
nary disc or a common envelope (Bartos et al 2017; Woosley 2016; Stone et al 2017).
For more general introductory articles on
GW
generation, detection and astrophysics,
we point readers to Blanchet (2014); Pitkin et al (2011); Sathyaprakash and Schutz
(2009).
Although our collaborations have amassed a great deal of experience with
GW
detectors and analysis, it is still difficult to make predictions for both improvements
in search methods and for the rate of progress for detectors which are not yet fully
installed or operational.
The scenarios of detector sensitivity evolution and observing
times given here should not be considered as fixed or firm commitments.
As the detectors’ construction and commissioning progress, we intend to release
updated versions of this article. This is the third version of the article, written to
coincide with the close of the second observing run (O2) of the advanced-detector era.
Changes with respect to the previous version (Aasi et al 2016) are given in Appendix A.
Progress has been made in the commissioning of the detectors. We include projections
for KAGRA for the first time; we also include results from the first observing run (O1)
and currently available results from O2.
2 Commissioning and observing phases
We divide the development of the GW observatories into three components:
Construction
includes the installation and testing of the detectors. This phase ends
with
acceptance
of the detectors. Acceptance means that the interferometers can
lock for periods of hours: light is resonant in the arms of the interferometer with
no guaranteed
GW
sensitivity.
Construction incorporates several short
engineering
runs
with no astrophysical output as the detectors progress towards acceptance. The
aLIGO construction project ended in March 2015. The construction of AdV was
completed at the end of 2016. KAGRA will be operational in its full configuration
by early 2019.
Commissioning
improves the detectors’ performance with the goal of reaching the
design sensitivity. Engineering runs in the commissioning phase allow us to
understand our detectors and analyses in an observational mode; these are not
intended to produce astrophysical results, but that does not preclude the possibility
of this happening.
2
Rather than proceeding directly to design sensitivity before
making astrophysical observations, commissioning is interleaved with
observing
runs
.
2
The detection of GW150914 occurred in the engineering run ER8 immediately preceding the formal
start of O1.
4
KAGRA Collaboration, LIGO Scientific Collaboration and Virgo Collaboration
Observing
runs begin when the detectors have reached (and can stably maintain) a
significantly improved sensitivity compared with previous operation. Observing
runs will produce astrophysical results, direct detections from some
GW
sources
and upper limits on the rates or energetics of others. During the first two observing
runs (O1 and O2), exchange of
GW
candidates with partners outside the LIGO
Scientific Collaboration (
LSC
) and the Virgo Collaboration was governed by
memoranda of understanding (MOUs; Abadie et al 2012d; Aasi et al 2013b). From
the start of the third observing run (O3), all
GW
event candidates identified with
high confidence will be released immediately to the full astronomical community.
KAGRA will become a part of the global network with full data sharing, once
sensitivities comparable with aLIGO and AdV are achieved.
The progress in sensitivity as a function of time will influence the duration of the
observing runs that we plan at any stage. Commissioning is a complex process which
involves both scheduled improvements to the detectors and tackling unexpected new
problems. While our experience makes us cautiously optimistic regarding the schedule
for the advanced detectors, we are targeting an order of magnitude improvement in
sensitivity relative to the previous generation of detectors over a wider frequency band.
Consequently, it is not possible to make concrete predictions for sensitivity or duty
cycle as a function of time. We can, however, use our experience as a guide to plausible
scenarios for the detector operational states that will allow us to reach the desired
sensitivity. Unexpected problems could slow down the commissioning, but there is
also the possibility that progress may happen faster than predicted here. The schedule
of commissioning phases and observation runs will be driven by a cost–benefit analysis
of the time required to make significant sensitivity improvements. More information
on event rates could also change the schedule and duration of runs.
In Sect. 2.1 we present the commissioning plans for the aLIGO, AdV and KAGRA
detectors. A summary of expected observing runs is in Sect. 2.2.
2.1 Commissioning and observing roadmap
The anticipated strain sensitivity evolution for aLIGO, AdV and KAGRA is shown
in Fig. 1. As a standard figure of merit for detector sensitivity, we use the range, the
volume- and orientation-averaged distance at which a compact binary coalescence
consisting of a particular mass gives a matched filter signal-to-noise ratio (
SNR
) of
8
in a single detector (Finn and Chernoff 1993). We define
V
z
as the orientation-
averaged spacetime volume surveyed per unit detector time; for a population with a
constant comoving source-frame rate density,
V
z
multiplied by the rate density gives
the detection rate of those sources by the particular detector. We define the range
R
as the distance for which
(
4
π
/
3
)
R
3
=
V
z
. In Table 1 we present values of
R
for
different detector networks and binary sources. For further insight into the range, and a
discussion of additional quantities such as the median and average distances to sources,
please see Chen et al (2017). The
BNS
ranges, assuming two
1
.
4
M
neutron stars, for
the various stages of the expected evolution are provided in Fig. 1, and the
BNS
and
BBH ranges are quoted in Table 1.