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Impact of the Einstein Telescope’s duty cycle on the estimation of binary black hole parameters

Luca Negri1,2,*, Thomas C. K. Ng2,1, Thibeau Wouters1,2, Tim J. Kuhlbusch3, Harsh Narola1,2, Robin Chan4,5, Kailib Ryan Doney6,7, Francesco Cireddu7,8, Isaac C. F. Wong7,9 et al.

Fabian Gittins1,2, Peter T. H. Pang2,1, Anuradha Samajdar1,2, Achim Stahl3, Justin Janquart4,10, Chris Van Den Broeck1,2, and Tjonnie G. F. Li7,8,9

  • 1Institute for Gravitational and Subatomic Physics (GRASP), Utrecht University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
  • 2Nikhef, Science Park 105, 1098 XG Amsterdam, The Netherlands
  • 3Physics Institute IIIB, RWTH Aachen University, Sommerfeldstrasse 16, 52074 Aachen, Germany
  • 4Royal Observatory of Belgium, Avenue Circulaire, 3, 1180 Uccle, Belgium
  • 5Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, 9000 Ghent, Belgium
  • 6Department of Physics, Chinese University of Hong Kong, Sha Tin, Hong Kong
  • 7Leuven Gravity Institute, KU Leuven, Celestijnenlaan 200D Box 2415, 3001 Leuven, Belgium
  • 8Department of Physics and Astronomy, Laboratory for Semiconductor Physics, KU Leuven, B-3001 Leuven, Belgium
  • 9KU Leuven, Department of Electrical Engineering (ESAT), STADIUS Center for Dynamical Systems, Signal Processing and Data Analytics, B-3001 Leuven, Belgium
  • 10Centre for Cosmology, Particle Physics and Phenomenology - CP3, Université Catholique de Louvain, Louvain-La-Neuve, B-1348, Belgium

  • *Contact author: l.negri@uu.nl
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Phys. Rev. D 114, 082003 – Published 13 October, 2026

DOI: https://doi.org/10.1103/1zg7-sd8v

Abstract

The geometry of the Einstein Telescope, the proposed next-generation European gravitational-wave observatory, is yet to be finalized. Two competing designs are under consideration: a nested triangular configuration (ET-Δ) and two separated L-shaped detectors (ET-2L). Extensive prior comparisons of ET designs established the scientific landscape using the Fisher-information-matrix formalism and identified that duty-cycle-induced single-detector operation is precisely the regime where this approximation becomes less reliable, underscoring the need for a refined, principled treatment of the duty cycle. In this manuscript, we build on that foundation by revisiting the comparison with full Bayesian parameter estimation of gravitational-wave signals from binary black hole mergers, projected onto a simulated Einstein Telescope that incorporates a refined duty cycle modeled via continuous-time Markov chains and testing different detector maintenance strategies. We find that the redundancy inherent in the ET-Δ design enables it to maintain at least two operational detectors for the majority of the observing time, whereas the ET-2L configuration is often limited to a single detector. Crucially, we show that, during partial network operation, ET-Δ often outperforms ET-2L, and that the increased multidetector uptime translates into tighter constraints on the luminosity distance and source-frame component masses. Notably, this remains true even when gravitational-wave events have a lower signal-to-noise ratio in ET-Δ than in ET-2L.

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Phys. Rev. D 114, 082003– Published 13 October, 2026
  • Received 24 June 2026
  • Accepted 11 September 2026
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