Plasma lensing near the eclipses of the Black Widow pulsar B1957+20

ABSTRACT Recently, several eclipsing millisecond pulsars have been shown to experience strong and apparent weak lensing from the outflow of their ionized companions. Lensing can be a powerful probe plasma, with strongest lenses potentially resolving emission regions pulsars. Understanding in ‘laboratory-like’ conditions an pulsar may analogously applied fast radio bursts, many which reside dense, magnetized environments. We examined variable dispersion measure (DM), absorption, scattering, flux density original Black Widow PSR B1957+20 through eclipse at Arecibo Observatory $327\, {\rm MHz}$. discovered clear evidence two regimes lensing, strong, weak. show that variations apparently regime modelled directly DM, using geometric optics. The mean effective velocities ingress, $(954\pm 99)\, km\, s^{-1}}$, egress $(604\pm 47)\, s^{-1}}$ cannot explained by orbital motions alone, but are consistent significant velocity material companion. also optics predict when where regime-change between occurs, argue is due averaging images. Our framework any source electron columns, measuring relative distances. In other pulsars, this provides unique opportunity companion velocity, principle independently constrain inclinations.