2020MNRAS.495.2777I

We comment on a recent study reporting evidence for the general relativistic Lense-Thirring secular precession of the inclination I of the orbital plane to the plane of the sky of the tight binary system PSR J1141-6545 made of a white dwarf and an emitting radiopulsar of comparable masses. The quadrupole mass moment Q₂^c and the angular momentum S^c of the white dwarf cause the detectable effects on I with respect to the present-day accuracy in the pulsar's timing. The history-dependent and model-dependent assumptions to be made on Q₂^c and S^c, required even just to calculate the analytical expressions for the resulting post-Keplerian precessions, may be deemed as too wide in order to claim a successful test of the Einsteinian gravitomagnetic effect. Moreover, depending on how Q₂^c is calculated, the competing quadrupole-induced rate of change, which is a major source of systematic uncertainty, may be up to ≲30-50 per cent of the Lense-Thirring effect for most of the allowed values in the 3D parameter space spanned by the white dwarf's spin period P_s, and the polar angles i_c, ζ_c of its spin axis. The possible use of the longitude of periastron p is investigated as well. It turns out that a measurement of its secular precession, caused, among other things, also by Q₂^c, S^c, could help in further restricting the permitted regions in the white dwarf's parameter space.