Pulsars and neutron stars/Pulsar rotation measures

Measuring pulsar rotation measures
Pulsar rotation measures (RMs) are measured by fitting the position angle of the linear polarization over a range of observing frequencies as:

$$\psi = {\rm RM} \lambda^2$$

where $$\lambda = c/f$$ where $$f$$ is the observing frequency.

Measured pulsar RMs vary, in part, because of the Earth's ionosphere. This ionospheric correction can be estimated using the International Reference Ionosphere (IRI) model.