Figure 2.

Panels of fixed θ_max,R depicting computed curves for the one-to-one coupling between eclipse fraction f_E and the shock stagnation point R₀ for PSR B1957+20 in the axisymmetric optically-thick shock scenario with a range of orbital inclinations i, as developed analytically in Appendix A. The panels depict successively higher values of θ_max,R from left to right, with the two rightmost panels prescribing values of θ_max,R that depend on R₀ as stated. The bold blue curve highlights the best-fit optical light curve modeling observational result i = 65° ± 2° in Reynolds et al. (2007), while other curves survey the viable lower and upper systematic bounds as presented in van Kerkwijk et al. (2011). Note that ζ ≈ i ≈ 85° is also found from favored outer-gap γ-ray pulsation fitting in Johnson et al. (2014). The mass ratio is fixed to q = 69.2 for all curves while the excluded region of R₀ indicate the companion and volumetric Roche lobe R_vL (q) radii (Eggleton 1983). Radio observations from Ryba & Taylor (1991) are illustrated with the horizontal lines. The red region below 600 MHz, where eclipses are to some degree symmetric, isolates roughly the region of validity of the axisymmetric calculation.