Sky localization of gravitational waves from eccentric binaries

TL;DR

The paper demonstrates that orbital eccentricity $\varepsilon$ in compact-binary mergers can substantially improve sky localization when localization algorithms are optimized for eccentric sources. It introduces a semi-Bayesian, eccentricity-optimized localization that conditions on eccentric-template outputs from a PSO-based eccentric search and samples extrinsic sky parameters in flat-sky coordinates, offering improvements over BAYESTAR for eccentric injections. Key contributions include quantitative reductions in 90% localization areas and the development of an eccentric early-warning framework with GPU-accelerated processing, evaluated in O4/O5-like detector networks. These results suggest significant gains for rapid electromagnetic follow-up and motivate incorporating eccentricity into real-time GW localization pipelines, scalable to larger detector networks and future observing runs.

Abstract

We demonstrate that the orbital eccentricity in compact binary mergers can be used to improve their sky localization using gravitational wave observations. Existing algorithms that conduct the localizations are not optimized for eccentric sources. We use a semi-Bayesian technique to carry out localizations of simulated sources recovered using a matched-filter search. Through these simulations, we find that if a non-negligible eccentricity is obtained during the detection, an eccentricity-optimized algorithm can significantly improve the localization areas compared to the existing methods. We also lay out the foundation for an eccentric early-warning system using the matched-filter search. The potential impact on the early-warning localization is investigated. We indicate a few possible cases of improvements while accounting for eccentricity toward any detectable eccentric neutron star binaries in the forthcoming observing scenarios of ground-based detectors. Improved localizations can be useful in effectually utilizing the capabilities of the follow-up facilities.

Figures (16)

• Figure 1: The projected power spectral densities (PSDs) of the Advanced LIGO in O4 and O5 are used for the simulations. Advanced Virgo and KAGRA are expected to be instrumental in detecting or refining the localizations of sources while advancing their sensitivities. Here all investigations are carried out with simulated Gaussian noise. We use a low-frequency cutoff of 20 Hz and 10 Hz respectively for the simulated O4 and O5 scenarios. The shaded regions mark the frequency ranges used for the simulated searches in this work.
• Figure 2: The coincident SNRs recovered by the PSO searches for simulated signals in the HL network having O4-like sensitivities. The searches are carried out in the frequency range of 20-512 Hz using the same datasets containing signals from spin-aligned eccentric BNSs immersed in Gaussian noise. The injected SNRs are computed at the injected parameters with a high-frequency cutoff of 2048 Hz. We use a fixed template-sampling for both the searches as described in the text. The eccentric search recovers all the injections that are also recovered by the aligned-spin search. The commonly found injections are shown here.
• Figure 3: PP-plots for the 3D localization parameters shown for the eccentric analysis of the simulated sources described in the Table. \ref{['tab:injpar']}. These are obtained without any non-trivial correction factor (or with a corresponding default value of 1), which is described later in the text. The gray regions represent the $1$, $2$, and $3\sigma$ uncertainty estimates obtained from beta distribution.
• Figure 4: Accuracy (left) and self-consistency (right) of the localization areas compared for the simulated eccentric sources. The solid curves are obtained using the estimated intrinsic source parameters with the PSO-based searches. The dashed curves are obtained using the injected source parameters. The probability plots on the right show that the credible sky areas are consistent at a 99.7% confidence.
• Figure 5: Cumulative historgrams showing the distribution of a credible (90%) area for the eccentric injections obtained with the eccentric and non-eccentric analyses.