The highest known magnetic fields found in pulsars are enough to change
the vacuum index of refraction in the region surrounding the stars. Since
the effect depends on the polarization of the light rays, it predicts more
sophisticated effects than for example what gravitational lensing does.
Not only will the apparent surface area grow, the effect will be polarization
dependant and therefore have a clear fingerprint that will allow the direct
measurement of a pulsar's magnetic field (and not an inferred one, as is
normally the case). In less impressive magnetic field strengths, that are
found in more common neutron stars, more subtle effects arise when taking
into consideration the rotation of the magnetosphere. Through predicted
polarization phase lags, the magnetospheres can in principle be “mapped”.
Summary of Achievements and Discoveries:
Plans for the Near Future:
Jeremy Heyl and Yoram Lithwick (at Caltech) on the lensing effects around
highly magnetized neutron stars. Jeremy Heyl on the polarization propagation
effects through a rotating magnetosphere, and recently, in collaboration
with Hari Kunduri who was a summer research stundent at CITA.
The Ray Tracing Algorithm used to image the neutron star. Rays are followed from the screen to the star (and not vice versa) using a Hamiltonian formalism for their propagation:
The next image is a sample result - this is how a neutron star with a very strong magnetic field looks like(when observed at an inclination of 45o). For the largest dipole fields known (of about 1015G), the effect is of order 5%.
The image of a lensed magnetar in one polarization
Movies showing Lensed Magnetars can be found here.
The polarization angle phase lag between different wavebands for the Crab pulsar: Plotted in the last figure is the polarization angle phase lag as a function of the waveband frequency and the time within the rotation period, assuming a Deutsch magnetic field configuration for the magnetosphere. By simultaneously measuring the polarization angle of the observed photons at different wavebands and different rotational phases of the neutron star, the structure of the magnetosphere can be mapped. Good UV and X-ray polarization measurements are required.
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