Prospects for Observing and Localizing Gravitational-Wave Transients with Advanced LIGO, Advanced Virgo and KAGRA (1304.0670v11)

Abstract: We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is BNS, NSBH, and BBH systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90\% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers.

• The paper forecasts significant improvements in detector sensitivity and localization accuracy across O3, O4, and O5 observing runs.
• It details specific performance benchmarks, predicting BNS ranges up to 190 Mpc and median localization areas shrinking to a few square degrees.
• The study highlights the pivotal role of an expanded detector network, including LIGO-India, in advancing multi-messenger astronomy and cosmic distance measures.

Overview of Observing and Localizing Gravitational-Wave Transients

The paper under discussion presents an in-depth analysis of the future observing capabilities and localization accuracy of the Advanced LIGO, Advanced Virgo, and KAGRA gravitational-wave detector networks. These detectors, crucial for the burgeoning field of gravitational-wave astronomy, enable the direct observation of cosmic phenomena such as black hole mergers and neutron star collisions.

The authors forecast a timeline extending through the third (O3), fourth (O4), and fifth (O5) observing runs. Each phase is characterized by upgrades aiming to enhance the sensitivity and localization capabilities of the network.

Observing Scenarios and Sensitivity Improvements

• O3 Run: The O3 observing run encompasses the utilization of a three-detector network (HLV) and the late inclusion of KAGRA, transforming the network into HLVK. The median sky localization area for binary systems was projected to improve from a few hundred to tens of square degrees.
• Sensitivity: The predicted BNS range for O3 was between 110-130 Mpc for LIGO, extending to 50 Mpc for Virgo. KAGRA’s early operational range was estimated to be 8-25 Mpc, primarily participating in the latter stages of O3.
• Detection Rates: During O3, the authors estimate approximately 17 binary black hole (BBH) coalescences and one binary neutron star (BNS) event per year with the HLV configuration. These estimations are informed by historical event rates and are subject to uncertainties in the astrophysical source models.

Improvements and Expectations for O4 and O5 Runs

• O4 Run: The paper anticipates substantial enhancements in sensitivity, with LIGO’s BNS range increasing to 160-190 Mpc and Virgo's to 90-120 Mpc. KAGRA's sensitivity is anticipated to show significant improvements, potentially achieving up to 130 Mpc. This increase in sensitivity is expected to result in more frequent detections and improved localization.
• O5 and LIGO-India: Looking ahead to O5, the introduction of the LIGO-India detector promises further advancements. The network is projected to achieve unprecedented precision in localization, covering median sky areas of just a few square degrees. This level of accuracy is critical for multi-messenger observations, facilitating the identification of electromagnetic counterparts.

Localization Capabilities and Astrophysical Implications

The localization of gravitational-wave sources is central to the observational process, enabling the identification of host galaxies and potential electromagnetic counterparts. The analysis indicates a marked improvement in localization accuracy with the expansion of the detector network. During O4, about 44% of BNS events are expected to be localized within a 20 square degree area.

The theoretical implications of these observations are profound. With a growing catalog of detections, the community will be equipped to refine models of binary formation, evolution, and their contribution to the observed population. Furthermore, improved localization supports the use of gravitational-wave events as standard sirens for measuring cosmic distances, thereby contributing to cosmology, particularly in determining the Hubble constant.

Future Prospects and Speculative Insights

As the network evolves, it will continuously redefine the landscape of astrophysics and facilitate numerous groundbreaking discoveries. Collaborations among gravitational wave detectors and other electromagnetic facilities will become more sophisticated, resulting in enhanced sensitivity to a variety of astronomical phenomena. The potential inclusion of space-based observatories could provide a complementary frequency range, advancing the domain of multiband gravitational-wave astronomy.

In conclusion, the paper meticulously outlines the plans for enhancing gravitational-wave observatories and provides a detailed forecast for future observing runs. These developments herald a new era of high-precision gravitational-wave science, poised to unravel further cosmic mysteries and deepen our understanding of the universe.