2023MNRAS.523.5064C

PSR J1757-1854 is one of the most relativistic double neutron star binary systems known in our Galaxy, with an orbital period of $P_\text{b}=4.4\, \text{h}$ 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 capitalize on this potential. We identify secular changes in the profile morphology and polarization 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 $w\ge 280\, \rm{km\,s}^{-1}$ 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 semimajor axis ($\dot{x}$) associated with Lense-Thirring precession is expected no earlier than 2031. Meanwhile, we anticipate a 3-σ measurement of the relativistic orbital deformation parameter δ_θ as soon as 2026.