Localizing binary neutron stars with the Einstein Telescope: a full Bayesian comparison of the triangular and 2L configurations
Abstract
The Einstein Telescope (ET), the European next-generation gravitational-wave observatory, is at a decisive stage: the choice of its detector configuration is still open, with profound implications for its scientific output. We provide a quantitative basis for this choice by comparing two candidate configurations at their proposed sites: the triangular design (Δ) at the Euregio Meuse-Rhine site, and the 2L design, with interferometers in Sardinia, Italy, and Lusatia, Germany. We present the first realistic estimates of sky-localization uncertainties for binary neutron star (BNS) mergers, moving beyond Fisher-matrix forecasts to full Bayesian parameter estimation that captures the multimodal structure of the sky posterior. We focus mainly on the high-frequency interferometers alone, providing an expected scenario for the first years of ET operations, as the more challenging low-frequency instruments will come online later. BNS injections span different sky positions and luminosity distances between 40 and 2000 Mpc, corresponding to signal-to-noise ratios (SNRs) from 12 to 720. Our analysis relaxes the long-wavelength approximation and includes Earth's rotation and higher-order modes, all of which improve sky localization. We find that the Δ configuration localizes low- and moderate-SNR sources in eight degenerate sky modes spread across both hemispheres and over the day and night sides of the Earth, with 90% credible areas reaching ∼ 2 × 104 deg2. In contrast, the 2L configuration recovers a single dominant mode that contains at least 50% of the posterior probability and is one to two orders of magnitude smaller in area. This represents a substantial advantage for multimessenger follow-up campaigns.
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BibTeX
@misc{santoliquido2026localizing,
title = {{Localizing binary neutron stars with the Einstein Telescope: a full Bayesian comparison of the triangular and 2L configurations}},
author = {Filippo Santoliquido and Jacopo Tissino and Marica Branchesi and Ulyana Dupletsa},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27081},
eprint = {2610.27081},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27081},
}
RIS
TY - UNPB
TI - Localizing binary neutron stars with the Einstein Telescope: a full Bayesian comparison of the triangular and 2L configurations
AU - Filippo Santoliquido
AU - Jacopo Tissino
AU - Marica Branchesi
AU - Ulyana Dupletsa
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.27081
UR - https://arxiv.org/abs/2610.27081
AB - The Einstein Telescope (ET), the European next-generation gravitational-wave observatory, is at a decisive stage: the choice of its detector configuration is still open, with profound implications for its scientific output. We provide a quantitative basis for this choice by comparing two candidate configurations at their proposed sites: the triangular design (Δ) at the Euregio Meuse-Rhine site, and the 2L design, with interferometers in Sardinia, Italy, and Lusatia, Germany. We present the first realistic estimates of sky-localization uncertainties for binary neutron star (BNS) mergers, moving beyond Fisher-matrix forecasts to full Bayesian parameter estimation that captures the multimodal structure of the sky posterior. We focus mainly on the high-frequency interferometers alone, providing an expected scenario for the first years of ET operations, as the more challenging low-frequency instruments will come online later. BNS injections span different sky positions and luminosity distances between 40 and 2000 Mpc, corresponding to signal-to-noise ratios (SNRs) from 12 to 720. Our analysis relaxes the long-wavelength approximation and includes Earth's rotation and higher-order modes, all of which improve sky localization. We find that the Δ configuration localizes low- and moderate-SNR sources in eight degenerate sky modes spread across both hemispheres and over the day and night sides of the Earth, with 90% credible areas reaching ∼ 2 × 10^4 deg^2. In contrast, the 2L configuration recovers a single dominant mode that contains at least 50% of the posterior probability and is one to two orders of magnitude smaller in area. This represents a substantial advantage for multimessenger follow-up campaigns.
ER -