PULSAR POLARIMETRIC OBSERVATIONS AT 10.55-GHZ

We present polarimetric observations of 19 pulsars, at 10.55 GHz. For most of them this is the highest frequency they have been observed pol arimetrically so far. We confirm that the average profile becomes prog ressively depolarized at high frequencies where emission is thought to originate from altitudes closer to the stellar polar cap. In most cas es studied the observed depolarization is associated with distortions of the polarization angle curve, indicating orthogonally or quasiortho gonally polarized emission. However, in some rare cases severe depolar ization is observed which is not associated with such distortions, imp lying a different depolarization mechanism. An anti-correlation has be en found between the depolarization index and the accelerating potenti al above the polar cap surface, which probably influences the elementa ry beaming of curvature radiation. Weak correlations were found betwee n the depolarization index and those parameters that characterize the geometry of the emission region, with the core width correlating most strongly. Two of the pulsars in our sample exhibit mode changes. The i ntensity mode changes are more remarkable than those at lower frequenc ies, whereas the associated polarization mode changes are less frequen cy dependent.