In this paper we have constrained the size of the pulsar emission region using high frequency observations made with the Effelsberg radio telescope. Our results indicate that the radiation is created close the neutron star. Close to the neutron star surface, the emission characteristics might be affected by the presence of magnetic multipoles, resulting in possible deviations of the polarisation angle swing curve from the expected rotating vector model (Radhakrishnan & Cooke 1969), peculiar profile developments or unexplainable timing results. We note that recent results indeed indicate a deviation from a purely dipolar magnetic field in the emission region of millisecond pulsars (e.g. Xilouris & Kramer 1996 or Navarro 1996, but see also Gil 1996), which has been previously expected by various authors (e.g. Ruderman 1991). Our presented data on long period pulsars, however, prove that such phenomena are certainly not observed at these high frequencies. This is in contrast to, for instance, the results of Davies et al. (1984) or Kuzmin et al. (1986). In particular, our observations of B2020+28, where an analysis has only included a fit of the pulse phase, suggest that previous results were probably influenced by instrumental effects. We therefore conclude that higher order magnetic multipoles are not existing in the emission region of long period pulsars.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998