The double neutron star PSR J1946+2052

I. Masses and tests of general relativity

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53131 Bonn, Germany
³ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
⁴ University of New Mexico, Department of Physics and Astronomy, University of New Mexico, 210 Yale Blvd NE, Albuquerque, NM 87106, USA
⁵ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, China
⁶ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, M13 9PL Manchester, UK
⁷ Cornell Centre for Astrophysics and Planetary Science and Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
⁸ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain
⁹ Institut d’Estudis Espacials de Catalunya (IEEC), Carrer Gran Capità 2–4, 08034 Barcelona, Spain
¹⁰ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
¹¹ Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Rd., Vancouver BC V6T 1Z1, Canada
¹² Cornell Center for Advanced Computing, Cornell University, Ithaca, NY 14853, USA
¹³ South African Radio Astronomy Observatory, Liesbeek House, River Park, Cape Town 7700, South Africa
¹⁴ Department of Physics and Astronomy, Franklin and Marshall College, P.O. Box 3003 Lancaster, PA 17604, USA
¹⁵ ASTRON, the Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
¹⁶ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁷ Department of Physics and Astronomy and Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV 26506-6315, USA
¹⁸ Qilu Normal University, College of Physics and Electronic Engineering, No. 2 Wenbo Road, Zhangqiu District, Jinan, China
¹⁹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150, Science 1-Street, Urumqi, Xinjiang 830011, China
²⁰ National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China

^⋆ Corresponding authors: menglingqi@nao.cas.cn, zhuww@nao.cas.cn

Received: 27 May 2025
Accepted: 4 October 2025

Abstract

Aims. Double neutron star (DNS) systems are superb laboratories for testing theories of gravity and constraining the equation of state of ultra-dense matter. PSR J1946+2052 is a particularly intriguing DNS system due to its orbital period (1h 53 m), as it is the shortest among all DNS systems known in our Galaxy.

Methods. We aim to conduct high-precision timing of PSR J1946+2052 to determine the masses of the two neutron stars in the system, test general relativity (GR), and assess the system’s potential for future measurement of the moment of inertia of the pulsar.

Results. We analysed seven years of timing data from the Arecibo 305-m radio telescope, the Green Bank Telescope, and the Five-hundred-meter Aperture Spherical radio Telescope. The data processing accounted for dispersion measure variations and relativistic spin precession-induced profile evolution. We employed both theory-independent (DDFWHE) and GR-dependent (DDGR) binary models to measure the spin parameters, kinematic parameters, and orbital parameters.

Results. The timing campaign resulted in the precise measurement of five post-Keplerian parameters, which yield very precise masses for the system (total mass M = 2.531858(60) M_⊙, companion mass M_c = 1.2480(21) M_⊙, and pulsar mass M_p = 1.2838(21) M_⊙), and three tests of GR. One of these tests is the second-most precise test of the radiative properties of gravity to date. The intrinsic orbital decay, Ṗ_b,int = −1.8288(16) × 10⁻¹², s s⁻¹, represents 1.00005(91) of the GR prediction, indicating that the theory has passed this stringent test. The other two tests of the Shapiro delay parameters have precisions of 6% and 5%, respectively. This is caused by the moderate orbital inclination of the system, ∼74°. The measurements of the Shapiro delay parameters also agree with the GR predictions. Additionally, we analysed the higher-order contributions of ω˙, including the Lense-Thirring contribution. Both the second post-Newtonian and the Lense-Thirring contributions are larger than the current uncertainty of ω˙ (δω˙ = 4 × 10⁻⁴ deg yr⁻¹), leading to the higher-order correction for the total mass.