Investigating the effect of sensitivity of KAGRA on sky localization of gravitational-wave sources from compact binary coalescences

TL;DR

Adding KAGRA to the gravitational-wave detector network improves sky localization and detection rates for binary neutron star mergers, even at modest sensitivities, by providing new baselines and directional information.

Contribution

This study systematically quantifies KAGRA's impact on sky localization and detection rates within the LIGO-Virgo-KAGRA network using injection simulations and a coherence-based localization framework.

Findings

KAGRA improves sky localization even at current sensitivity (~10 Mpc).

Higher sensitivity increases localization accuracy and detection rates.

KAGRA's inclusion enhances network performance through geometric complementarity.

Abstract

The addition of KAGRA to the global gravitational-wave detector network introduces new baselines and complementary antenna response patterns that can enhance sky localization for compact binary coalescences. We investigate KAGRA's role in the LIGO-Virgo-KAGRA network using a systematic injection study of binary neutron star signals. Sky maps are constructed with a radiometric, coherence-based framework, allowing isolation of geometric and timing contributions from individual detectors. Localization performance is quantified using the fraction of events localized within $100~\mathrm{deg}^2$, cumulative area distributions, and the median $90%$ credible region. We also assess KAGRA's impact on detection rates by varying its sensitivity over a wide range. Even at its current sensitivity of $\sim10~\mathrm{Mpc}$, KAGRA provides measurable improvements by breaking degeneracies through additional baselines and directional constraints. As sensitivity increases, improvements in signal-to-noise ratio and timing precision lead to substantial reductions in localization area. We identify a binary neutron star range of $\sim30~\mathrm{Mpc}$ as a practical benchmark for reliable localization suitable for electromagnetic follow-up, noting this as a conservative estimate. In addition, KAGRA increases the number of detectable events by enabling lower signal-to-noise detections. These results demonstrate that even a modest-sensitivity detector can significantly enhance network performance through geometric complementarity, highlighting the importance of a geographically distributed network for multimessenger gravitational-wave astronomy.