  In the current work we explore the applicability of standard theoretical
models of accretion to the observed properties of M51 ULX-7. The spin-up rate
and observed X-ray luminosity are evidence of a neutron star with a surface
magnetic field of $2-7\times10^{13}$ G, rotating near equilibrium. Analysis of
the X-ray light-curve of the system (Swift/XRT data) reveals the presence of a
$\sim$39 d super-orbital period. We argue that the super-orbital periodicity is
due to disc precession, and that material is accreted onto the neutron star at
a constant rate throughout it. Moreover, by attributing this modulation to the
free precession of the neutron star we estimate a surface magnetic field
strength of $3-4\times10^{13}$ G. The agreement of these two independent
estimates provide strong constraints on the surface polar magnetic field
strength of the neutron star.
