EDP Sciences
Free Access
Volume 421, Number 2, July II 2004
Page(s) 681 - 691
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361:20040228

A&A 421, 681-691 (2004)
DOI: 10.1051/0004-6361:20040228

Ellipticity and deviations from orthogonality in the polarization modes of PSR B0329+54

R. T. Edwards1 and B. W. Stappers1, 2

1  Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2  Stichting ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands

(Received 9 February 2004 / Accepted 26 March 2004 )

We report on an analysis of the polarization of single pulses of PSR B0329+54 at 328 MHz. We find that the distribution of polarization orientations in the central component diverges strongly from the standard picture of orthogonal polarization modes (OPMs), making a remarkable partial annulus on the Poincaré sphere. A second, tightly clustered region of density appears in the opposite hemisphere, at a point antipodal to the centre of the annulus. We argue that this can be understood in terms of birefringent alterations in the relative phase of two elliptically polarized propagation modes in the pulsar magnetosphere (i.e. generalised Faraday rotation). The ellipticity of the modes implies a significant charge density in the plasma, while the presence of both senses of circular polarization, and the fact that only one mode shows the effect, supports the view that refracted ordinary-mode rays are involved in the production of the annulus. At other pulse longitudes the polarization (including the circular component) is broadly consistent with an origin in elliptical OPMs, shown here quantitatively for the first time, however considerable non-orthogonal contributions serve to broaden the orientation distribution in an isotropic manner.

Key words: plasmas -- polarization -- stars: pulsars: individual: PSR B0329+54 -- waves

Offprint request: R. T. Edwards, redwards@science.uva.nl

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© ESO 2004

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