What does this equation mean?

The way you weigh a neutron star from a radio telescope, with no direct access to the star at all, is to time its pulses with enough precision to catch general relativity bending them. In a binary system seen close to edge-on, radio pulses from the neutron star are delayed by a few extra microseconds each orbit as they pass close to the companion star, because the companion’s gravity curves the spacetime the pulse crosses. The delay as a function of orbital phase $\phi$ is standardly written $\Delta_S(\phi) = -2r\,\ln\!\left[1 - s\sin\phi\right]$. where the “range” parameter r is set directly by the companion’s mass and the “shape” parameter s by the orbit’s inclination. Because r and s are measured independently of the pulsar’s own mass, and Kepler’s laws already fix the total system mass from the orbital period and velocity, a sufficiently edge-on, sufficiently precisely timed binary hands over both masses at once — no assumptions about the neutron star’s interior required. The catch is precision: resolving a mass difference of a few hundredths of a solar mass means resolving a timing residual measured in tens of nanoseconds across years of observation, which is why the equipment built for this work is built around atomic-clock frequency standards and years of accumulated data rather than any single observation.