Variations ofP₂in subpulse drifting pulsars

Abstract

We develop a model for subpulse separation period, P 2 , taking into account both the apparent motion of the visible point as a function of pulsar phase, ψ, and the possibility of abrupt jumps between different rotation states in non-corotating pulsar magnetospheres. We identify three frequencies: (i) the spin frequency of the star, (ii) the drift frequency of the magnetospheric plasma in the source region, and (iii) the angular frequency of the visible point around its trajectory. We show how the last of these, which is neglected in traditional models by implicitly assuming the line of sight through the center of the star, affects the interpretation of P 2 . We attribute the subpulse structure to emission from m anti-nodes distributed uniformly in azimuthal angle about the magnetic axis. We show that variations of P 2 as a function of rotational phase or observing frequency arise naturally when the motion of the visible point is taken into account. We discuss possible application of our model in signifying overall field-line distortion at the emitting region. Abrupt changes in P 2 can occur during state switching in the magnetosphere. We demonstrate that the unique value of P 2 in each rotation state can be used, in principle, to relate the rotation state of the magnetospheres to subpulse drifting.

PSR B0943+10: low-frequency study of subpulse periodicity in the Bright mode with LOFAR

“…This variation may stem from the bias to phase track caused by incoherent mixing of two linear polarisation modes of variable relative strength (Rankin & Suleymanova 2006), each mode corresponding to a separate set of sparks shifted in azimuth with respect to each other (DR01). If real, the variations of P2 may be linked to the changing plasma density in the magnetosphere through the motion of the visibility point (Yuen et al 2016).…”

Low-frequency Observations of the Subpulse Drifter PSR J0034−0721 with the Murchison Widefield Array

“…However, exactly the opposite is observed in the P 2 of PSR J0034−0721, so aberration effects cannot be invoked to explain it. Another possible explanation is the motion of the visible point as discussed by Yuen & Melrose (2014) and Yuen et al (2016), which takes into account the direction of the dipolar magnetic field at the emission site, an effect that has traditionally been neglected in the interpretation of P 2 measurements. They showed that measurements of P 2 can dramatically underestimate the true subbeam separation when the angle between the rotation and magnetic axes, α, is sufficiently small, which is believed to be the case for PSR J0034−0721 (e.g.…”

On the Geometry of Curvature Radiation and Implications for Subpulse Drifting

“…An important feature of the geometric model is the inclusion of the time taken for the spark information to reach the visible point, a non-negligible time, which to our knowledge is entirely lacking in other models of carousel behaviour. The quantity P 2 , which measures the elapsed time between the observation of two adjacent sparks, must therefore include not only AR effects and continuous carousel rotation (affecting the apparent spacing between the sparks, a theme discussed in Yuen et al 2016), but also the difference of path lengths of the respective particle trajectories. The length of the trajectories traced by particles in the IF ( ) are necessarily different from the path length along the magnetic field lines on which they reside-rotation effects should not be neglected.…”

“…The rotation matrices are given many times in the literature, and are not repeated here. For example, the Appendix of Yuen et al (2016) includes the relevant transformation matrices, as well as the matrix used to convert between Cartesian and spherical polar coordinates, which is also used in this work to Taylor expand about the magnetic axis (i.e. about θ = 0).…”