Complex emission patterns: fluctuations and bistability of polar-cap potentials

Abstract

Development of the ion-proton pulsar model extends it to the limit of large unscreened polar-cap potentials, for example, as in the Vela pulsar, in which ion charges differ only by small increments from their complete screening values. It is shown that the atomic number Z of an ion following its passage from the canonical Z 0 = 26 value through the electromagnetic shower region to the surface is not necessarily timeindependent but can vary between fixed limits in an irregular or quasi-periodic way in a characteristic time of the order of 10 4 s. Thus at a certain Z the system may transition to an unstable state of higher electric potential and it is argued that this is the physical basis for mode-changes, long-term nulls, periodic or otherwise. The model requires an orientation of magnetic dipole moment relative to rotational spin giving a positive corotational charge density. Success of the model would fix the particle composition of the remaining parts of the magnetosphere, including the Y-point and is therefore relevant to X-ray and γ-ray emission processes.

Investigation of Nulling and Subpulse-drifting Properties of PSR J1649+2533 with FAST

“…Because the number of pulse-nulling pulsars that have been observed and studied is relatively small compared to all known pulsars, the physical origin of pulse nulling in pulsars is not yet fully understood. Several previous studies have suggested that certain factors may lead to the occurrence of pulse nulling (Jones 1981;Filippenko & Radhakrishnan 1982;Zhang et al 1997;Geppert et al 2003Geppert et al , 2021Timokhin 2010;Jones 2020), including the failure of particle production in the polar cap region, the loss of coherence for relativistic particles, the instability of magnetic fields, and changes in the magnetosphere configurations and radiation mechanisms of the pulsar. It should be pointed out that the periodic pulse nulling may be a common occurrence in pulse-nulling pulsars.…”

The Single-pulse Observation of PSR B2111+46 with the Five-hundred-meter Aperture Spherical Radio Telescope

“…The origin of the pulse nulling of pulsars is not clear. Some studies hypothesized tgat the pulse nulling may be caused by the failure of particle production in the polar cap region (Jones 1981), the loss of coherence for the relativistic particles (Filippenko & Radhakrishnan 1982), the instability of the magnetic field (Geppert et al 2003), the change in the magnetosphere configurations (Timokhin 2010;Geppert et al 2021), as well as the radiation mechanism (Jones 1981;Zhang et al 1997;Jones 2020). The periodic nulls may be prevalent in many pulsars.…”

Nulling and subpulse drifting in PSR J1727-2739

“…In the original carousel model, the drift rate remains constant, and thus it is difficult to explain the observed multiple drift modes in a pulsar based on the original carousel model. There are several models exploring the mode changing behaviour in pulsars, such as reconfiguration of pulsar magnetosphere (Timokhin 2010), multiple magnetospheric states incorporating the apparent motion of the visible point (Yuen 2019), the ion-proton pulsar polar cap model (Jones 2020) and the partially screened gap (PSG) model (Gil et al 2003;Szary et al 2015) in which the perturbations in the magnetic field due to Hall and thermal drift oscillations change the sparking configuration (Geppert et al 2021). To explain the three distinct drift modes observed in the conal triple pulsar PSR B1918+19 in the carousel framework, Rankin et al (2013) explored the view that the observed drift bands result from the first-order alias of a faster drift of subbeams equally spaced around the cones.…”