Long-term timing of the relativistic binary PSR J1906+0746

We conducted a timing analysis of over 18 yr of data on the young (τ_c = 112 kyr, P = 114 ms) relativistic binary PSR J1906+0746, using six radio telescopes: Arecibo, FAST, Green Bank, Lovell, MeerKAT, and Nançay. This pulsar is known to orbit a compact high-mass companion with a period of 3.98h in a mildly eccentric orbit (e = 0.085). By combining all data and maintaining a coherent timing solution over the full span, we obtained a more precise measurement of the advance of periastron, ω̇ = 7.5841(2) deg yr^-1, the Einstein delay, γ = 4.59(2) × 10^-4s, and the secular change in orbital period, Ṗ_b = -5.65(2) × 10^-13 ss^-1. Assuming the validity of general relativity, we obtain a total mass of 2.6133(1) M_⊙ and component masses of 1.316(5) M_⊙ for the pulsar and 1.297(5) M_⊙ for the companion, consistent with a double neutron star system. However, when fitting for the secular change in the projected semimajor axis we obtain ẋ = -1.8(6) × 10^-13 ss^-1. The component masses are shifted by ∼ 3.5σ, which is expected from the correlation of ẋ and γ. The ẋ has a similar magnitude to that observed in PSR J1141–6545, which is due to spin–orbit coupling; if confirmed, it would indicate that, as in the latter system, the companion of the PSR J1906+0746 system is a massive fast-rotating white dwarf formed before the pulsar. Additionally, we report and characterize a large glitch near MJD 56664, with a fractional frequency increase comparable to those observed in the Vela pulsar.