On Pair Production in the Crab Pulsar

We consider the widespread assumption that coherent pulsar radio emission is based on extended pair production leading to plasma densities highly exceeding the Goldreich-Julian density. We show as an example that the observed low frequency (160 MHz) emission of the Crab pulsar is incompatible to the model of extended pair production. Our results rule out significant pair production if a plasma process is responsible for coherence and the radio emission originates from inside the light cylinder.Comment: accepted for publication in ApJ Letters; 4 pages, no figure

Geodetic Precession and the Binary Pulsar B1913+16

A change of the component separation in the profiles of the binary pulsar PSR B1913+16 has been observed for the first time (Kramer 1998) as expected by geodetic precession. In this work we extend the previous work by accounting for recent data from the Effelsberg 100-m telescope and Arecibo Observatory and testing model predictions. We demonstrate how the new information will provide additional information on the solutions of the system geometry.Comment: 2 pages, 1 figure, IAU 177 Colloquium: Pulsar Astronomy - 2000 and Beyon

Simultaneous single-pulse observations of radio pulsars: II. Orthogonal polarization modes in PSR B1133+16

In this paper, we present a study of orthogonal polarization modes in the radio emission of PSR B1133+16, conducted within the frame of simultaneous, multi-frequency, single-pulse observations. Simultaneously observing at two frequencies (1.41 GHz and 4.85 GHz) provides the means to study the bandwidth of polarization features such as the polarization position angle. We find two main results. First, that there is a high degree of correlation between the polarization modes at the two frequencies. Secondly, the modes occur more equally and the fractional linear polarization decreases towards higher frequencies. We discuss this frequency evolution and propose propagation effects in the pulsar magnetosphere as its origin.Comment: Accepted for publication in A&A. 5 pages, 4 figure

Toward An Empirical Theory of Pulsar Emission VIII: Subbeam Circulation and the Polarization-Modal Structure of Conal Beams

The average polarization properties of conal single and double profiles directly reflect the polarization-modal structure of the emission beams which produce them. These average properties require that the circulating subbeam systems which produce conal beams entail paired PPM and SPM emission elements which are offset from each other in both magnetic azimuth and magnetic colatitude. A clear delineation of the modal polarization topology of the conal beam promises to address fundamental questions about the nature and origin of this modal emission--and the modal parity at the outer beam edges is a fact of considerable significance. The different angular dependences of the modal ``beamlets'' suggests that the polarization modes are generated via propagation effects. This argument may prove much stronger if the modal emission is fundamentally only partially polarized. Several theories now promise quantitative comparison with the observations.Comment: Submitted to Astrophysical Journa

Comparing Geometrical and Delay Radio Emission Heights in Pulsars

We use a set of carefully selected published average multifrequency polarimetric observations for six bright cone dominated pulsars and devise a method to combine the multifrequency polarization position angle (PPA) sweep traverses. We demonstrate that the PPA traverse is in excellent agreement with the rotating vector model over this broad frequency range confirming that radio emission emanates from perfectly dipolar field lines. For pulsars with central core emission in our sample, we find the peak of central core component to lag the steepest gradient of the PPA traverse at several frequencies. Also significant frequency evolution of the core width is observed over this frequency range. The above facts strongly suggest: (a) the peak core emission does not lie on the fiducial plane containing the dipole magnetic axis and the rotation axis, and (b) the core emission does not originate from the polar cap surface.Comment: Accepted for publication in Astronomy and Astrophysic