The Optics of Neutron-Star Magnetospheres

Extremely strong magnetic fields change the vacuum index of refraction. This induces a lensing effect that is not unlike the lensing phenomenon in strong gravitational fields. The main difference between the two is the polarization dependency of the magnetic lensing, a behaviour that induces a handful of interesting effects. The main prediction is that the thermal emission of neutron stars with extremely strong magnetic fields is polarized independent of surface composition - up to a few percent for the largest fields known. The difference is the indices of refraction also decouples the propagation modes through the magnetosphere. For sufficiently high frequencies, this decoupling is independent of the properties of the magnetospheric plasma. This QED effect may allow observations to distinguish between different pulsar emission mechanisms and to reconstruct the structure of the magnetosphere. their magnetospheres and the emission region.