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X-Ray Polarimetry Workshop SLAC, Stanford, California 9-11 February 2004 |
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Polarization Properties of Rotation Powered Pulsars in Polar Cap Models
Alice
Harding
NASA Goddard Space Flight Center
Alice.K.Harding@nasa.gov
Alice K. Harding
Phase-resolved polarimetry of rotation-powered pulsars has had enormous diagnostic capability at radio and optical wavelengths and could also be a powerful diagnostic in the X-ray range. The pulsed non-thermal radiation from relativistic particles in the magnetosphere is tightly beamed along the neutron-star magnetic field lines and thus the emitted radiation is believed to be highly polarized either parallel or perpendicular to the field lines. Measurement of the polarization properties as a function of pulse phase can therefore provide a multidimensional mapping of the pulsar emission. In the `rotating vector' model, radiation originating near a magnetic pole is expected to show a characteristic S-shaped swing of the position angle vs. pulse phase. In this case it is possible to determine the magnetic inclination and viewing angles. Radiation originating further from the poles or further above the neutron star surface will have a more complex polarization signature, as a result of relativistic effects of aberration and time-of-flight delays. More extended emission regions may also cause depolarization of the signal. I will discuss predicted polarization properties of pulsed emission in both traditional polar cap models, where radiation originates very the neutron star surface at the magnetic poles, and in more recently proposed polar slot gap models, where radiation originates over a range of altitudes from the pole to the speed-of-light cylinder. The two types of model should be readily distinguishable with phase-resolved polarimetry.
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For more information, contact
Jennifer Formichelli |
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