Observing Capabilities¶
This section summarizes the observing capabilities of the global gravitationalwave detector network as of early 2019. This as a quick reference to the anticipated commissioning and observing schedule, sensitivity to gravitationalwave transients, and sky localization accuracy, as described in the following external documents:
White Paper 1 on gravitationalwave data analysis and astrophysics
Living Review 2 (see preprint of revised version 3) on prospects for observing and localizing gravitationalwave transients with Advanced LIGO, Advanced Virgo, and KAGRA
Current O3 Schedule 4
Timeline¶
The gravitationalwave observing schedule is divided into Observing Runs or epochs of months to years of operation at fixed sensitivity, down time for construction and commissioning, and transitional Engineering Runs between commissioning and observing runs. The longterm observing schedule is shown below. Since BNS mergers are a wellstudied class of gravitationalwave signals, this figure gives the BNS range for each observing run.
Engineering Run 14 (ER14) started on 20190304. The transition into Observing Run 3 (O3) occurred on 20190401. O3 had been scheduled to end on 20200430, but was suspended early on March 27, 2020, due to the COVID19 pandemic 5. When it becomes safe to resume normal activities, there may be a short period of additional O3 observations before an extended shutdown to prepare for the next observing run (O4). Updates will be posted in this document as they become available.
During O3, we expect that three facilities (LHO, LLO, and Virgo) will observe for one year. It is possible that the Japanese KAGRA detector may come online and become part of the international gravitationalwave network at some point during O3. The nearterm observing schedule is shown below, reproduced from 4.
Live Status¶
There are a handful of public web pages that report live status of the LIGO/Virgo detectors and alert infrastructure.
 Detector Status Portal: Daily summary of detector performance.
 GWIStat: Realtime detector up/down status.
 LIGO Data Grid Status: Live dashboard showing up/down status of the detectors and online analyses. Status of the LIGO/Virgo alert pipeline is indicated by the “EMFollow” box.
Sensitivity¶
The following O3 projections are adapted from the preprint version of the Living Review 3 on prospects for observing and localizing gravitationalwave transients with Advanced LIGO, Advanced Virgo, and KAGRA. The table below gives the range of each individual detector for BNS, NSBH, and BBH mergers, and unmodeled bursts.
Detector 
Range (Mpc) 


BNS 
NSBH 
BBH 
Burst 

LIGO 
110–130 
190240 
9901200 
80–90 
Virgo 
50 
90 
500 
35 
KAGRA 
8–25 
1545 
80260 
525 
These ranges are given for the following fiducial signals:
 BNS
A merger of two \(1.4 M_\odot\) NSs.
 NSBH
 BBH
A merger of two \(30 M_\odot\) BHs.
 Burst
A monochromatic signal at a frequency of 140 Hz carrying an energy of \(E_\mathrm{GW}=10^{2} M_\odot c^2\).
Note
The range is defined in relation to the sensitive volume, or the surveyed spacetime volume per unit detector time. The range is neither a luminosity distance nor a comoving distance.
Detection Rate and Localization Accuracy¶
Here we provide predicted detection rates, distances, and localization uncertainties for BNS, NSBH, and BBH mergers in O3 and O4, based on a Monte Carlo simulation of detection and localization of events in O3 and O4. Details of the simulation are described in 3.
Sky localization FITS files from these simulations are provided at https://git.ligo.org/emfollow/obsscenarios2019fitsfiles.
Summary Statistics¶
The table below summarizes the predicted detection rate and sky localization accuracy in O3 and O4. All values are given as a 5% to 95% confidence intervals.
Observing run 
Network 
Source class 


Merger rate per unit comoving volume per unit proper time
(Gpc^{3} year^{1},
lognormal uncertainty)


1103840 
0.601000 
25109 

Sensitive volume: detection rate / merger rate
(Gpc^{3}, Monte Carlo uncertainty)


O3 
HLV 
\(0.0033 ^{+0.00028} _{0.00026}\) 
\(0.02 ^{+0.0016} _{0.0015}\) 
\(0.34 ^{+0.026} _{0.025}\) 
O3 
HLVK 
\(0.0034 ^{+0.00028} _{0.00027}\) 
\(0.020 ^{+0.0016} _{0.0015}\) 
\(0.35 ^{+0.026} _{0.025}\) 
O4 
HLVK 
\(0.016 ^{+0.0014} _{0.0013}\) 
\(0.092 ^{+0.0077} _{0.0072}\) 
\(1.5 ^{+0.10} _{0.096}\) 
Annual number of detections
(lognormal merger rate uncertainty \(\times\) Poisson
counting uncertainty)


O3 
HLV 
\(1 ^{+12} _{1}\) 
\(0 ^{+19} _{0}\) 
\(17 ^{+22} _{11}\) 
O3 
HLVK 
\(1 ^{+12} _{1}\) 
\(0 ^{+19} _{0}\) 
\(18 ^{+22} _{12}\) 
O4 
HLVK 
\(10 ^{+52} _{10}\) 
\(1 ^{+91} _{1}\) 
\(79 ^{+89} _{44}\) 
Median luminosity distance
(Mpc, Monte Carlo uncertainty)


O3 
HLV 
\(110 ^{+3.7} _{4.6}\) 
\(210 ^{+6.6} _{8.2}\) 
\(640 ^{+29} _{19}\) 
O3 
HLVK 
\(110 ^{+3.8} _{4.2}\) 
\(210 ^{+7.7} _{6.9}\) 
\(630 ^{+25} _{23}\) 
O4 
HLVK 
\(170 ^{+6.3} _{4.8}\) 
\(330 ^{+7.0} _{13}\) 
\(990 ^{+35} _{29}\) 
Median 90% credible area
(deg^{2}, Monte Carlo uncertainty)


O3 
HLV 
\(270 ^{+34} _{20}\) 
\(330 ^{+24} _{31}\) 
\(280 ^{+30} _{23}\) 
O3 
HLVK 
\(190 ^{+36} _{30}\) 
\(240 ^{+37} _{44}\) 
\(220 ^{+33} _{24}\) 
O4 
HLVK 
\(33 ^{+4.9} _{5.3}\) 
\(50 ^{+8.0} _{8.4}\) 
\(41 ^{+7.2} _{5.7}\) 
Median 90% credible comoving volume
(10^{3} Mpc^{3},
Monte Carlo uncertainty)


O3 
HLV 
\(120 ^{+19} _{24}\) 
\(860 ^{+150} _{150}\) 
\(16000 ^{+2200} _{2500}\) 
O3 
HLVK 
\(79 ^{+27} _{19}\) 
\(560 ^{+190} _{160}\) 
\(11000 ^{+2300} _{2300}\) 
O4 
HLVK 
\(52 ^{+9.9} _{9.1}\) 
\(430 ^{+100} _{78}\) 
\(7700 ^{+1500} _{920}\) 
Merger rate per unit comoving volume per unit proper time is the astrophysical rate of mergers in the reference frame that is comoving with the Hubble flow. It is averaged over a distribution of masses and spins that is assumed to be nonevolving.
Caution
The merger rate per comoving volume should not be confused with the binary formation rate, due to the time delay between formation and merger.
It should also not be confused with the merger rate per unit comoving volume per unit observer time. If the number density per unit comoving volume is \(n = dN / dV_C\), and the merger rate per unit proper time \(\tau\) is \(R = dn/d\tau\), then the merger rate per unit observer time is \(R / (1 + z)\), with the factor of \(1 + z\) accounting for time dilation.
See 9 for further discussion of cosmological distance measures as they relate to sensitivity figures of merit for gravitationalwave detectors.
For BNS and BBH, the merger rate is inferred from fitting the observed population of LIGO/Virgo events in O1 and O2 67. For NSBH, the merger rate is taken from 8. The quoted confidence interval assumes that the uncertainty in the rate has a lognormal distribution.
Sensitive volume is the quotient of the rate of detected events per unit observer time and the merger rate per unit comoving volume per unit proper time. The definition is given in the glossary entry for sensitive volume. To calculate the detection rate, multiply the merger rate by the sensitive volume.
The quoted confidence interval represents the uncertainty from the Monte Carlo simulation.
Annual number of detections is the number of detections in one calendar year of observation. The quoted confidence interval incorporates both the lognormal distribution of the merger rate and Poisson counting statistics, but does not include the Monte Carlo error (which is negligible compared to the first two sources of uncertainty).
The remaining sections all give median values over the population of detectable events.
Luminosity distance is the luminosity distance in Mpc of detectable events. The quoted confidence interval represents the uncertainty from the Monte Carlo simulation.
90% credible area is the area in deg\(^2\) of the smallest (not necessarily simply connected) region on the sky that has a 90% chance of containing the true location of the source.
90% credible volume is the comoving volume enclosed in the smallest region of space that has a 90% chance of containing the true location of the source.
Cumulative Histograms¶
Below are cumulative histograms of the 90% credible area, distance, and 90% credible comoving volume of detectable events in O3 and O4.
 1
LIGO Scientific Collaboration & Virgo Collaboration 2019, The LSCVirgo White Paper on Gravitational Wave Data Analysis and Astrophysics. LIGOT1900541v2
 2
Abbott, B. P., Abbott, R., Abbott, T. D., et al. 2018, Living Rev. Rel., 21, 3. doi:10.1007/s4111401800129
 3(1,2,3)
LIGO Scientific Collaboration & Virgo Collaboration 2019, Prospects for Observing and Localizing GravitationalWave Transients with Advanced LIGO, Advanced Virgo and KAGRA. arXiv:1304.0670
 4(1,2)
LIGO Scientific Collaboration & Virgo Collaboration 2019, Current O3 Schedule. LIGOG1901531v3
 5
LIGO Laboratory 2020, LIGO Ending O3 Observations. LIGOL2000133v3
 6
LIGO Scientific Collaboration & Virgo Collaboration 2019, Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo. Astropys. J. Lett., 882, 24. doi:10.3847/20418213/ab3800
 7
LIGO Scientific Collaboration & Virgo Collaboration 2019, GWTC1: A GravitationalWave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs. Phys. Rev. X, 9, 031040. doi:10.1103/PhysRevX.9.031040
 8
LIGO Scientific Collaboration & Virgo Collaboration 2010, Predictions for the rates of compact binary coalescences observable by groundbased gravitationalwave detectors. Class. Quantum Grav., 27, 173001. doi:10.1088/02649381/27/17/173001
 9
Chen, H.Y., Holz, D. E., et al. 2017, Distance measures in gravitationalwave astrophysics and cosmology. arXiv:1709.08079