New constraints on the kinematic, relativistic and evolutionary properties of the PSR J1757−1854 double neutron star system

PSR J1757−1854 is one of the most relativistic double neutron star binary systems known in our Galaxy, with an orbital period of Pb=4.4hr and an orbital eccentricity of e=0.61. As such, it has promised to be an outstanding laboratory for conducting tests of relativistic gravity. We present the results of a 6-yr campaign with the 100-m Green Bank and 64-m Parkes radio telescopes, designed to capitalise on this potential. We identify secular changes in the profile morphology and polarisation of PSR J1757−1854, confirming the presence of geodetic precession and allowing the constraint of viewing geometry solutions consistent with General Relativity. We also update PSR J1757−1854's timing, including new constraints of the pulsar's proper motion, post-Keplerian parameters and component masses. We conclude that the radiative test of gravity provided by PSR J1757−1854 is fundamentally limited to a precision of 0.3 per cent due to the pulsar's unknown distance. A search for pulsations from the companion neutron star is also described, with negative results. We provide an updated evaluation of the system's evolutionary history, finding strong support for a large kick velocity of w≥280km s−1 following the second progenitor supernova. Finally, we reassess PSR J1757−1854's potential to provide new relativistic tests of gravity. We conclude that a 3-σ constraint of the change in the projected semi-major axis (x˙) associated with Lense-Thirring precession is expected no earlier than 2031. Meanwhile, we anticipate a 3-σ measurement of the relativistic orbital deformation parameter δθ as soon as 2026.