Spark Model for Pulsar Radiation Modulation Patterns

Abstract

A non-stationary polar gap model first proposed by Ruderman & Sutherland (1975) is modified and applied to spark-associated pulsar emission at radio wave-lengths. It is argued that under physical and geometrical conditions prevailing above pulsar polar cap, highly non-stationary spark discharges do not occur at random positions. Instead, sparks should tend to operate in well determined preferred regions. At any instant the polar cap is populated as densely as possible with a number of two-dimensional sparks with a characteristic dimension as well as a typical distance between adjacent sparks being about the polar gap height. Our model differs, however, markedly from its original 'hollow cone' version. The key feature is the quasi-central spark driven by pair production process and anchored to the local pole of a sunspot-like surface magnetic field. This fixed spark prevents the motion of other sparks towards the pole, restricting it to slow circumferential drift across the planes of field lines converging at the local pole. We argue that the polar spark constitutes the core pulsar emission, and that the annular rings of drifting sparks contribute to conal components of the pulsar beam. We found that the number of nested cones in the beam of typical pulsar should not excced three; a number also found by Mitra & Deshpande (1999) using a completely different analysis.Comment: 31 pages, 8 figures, accepted by Ap

Statistics of the Drifting Subpulse Phenomenon

“…This is also a consequence of the Gil & Sendyk (2000) model. In the sparking gap model, the drifting phenomenon is associated with conal emission and therefore expected to be seen in pulsars with an on average higher modulation index.…”

“…sparks). The number of sparks that fits on the polar cap is quantified by the complexity parameter (Gil & Sendyk 2000), which is expected to be anti-correlated with the modulation index (Jenet & Gil 2003). The complexity parameter is a function of the pulse period and its derivative and its precise form depends on the model one assumes for the pulsar emission.…”

Vacuum gap model for PSR B0943+10

“…Following the original idea of RS75, Gil & Sendyk (2000; hereafter GS00) argued that the polar cap is populated with N max ∼ a 2 sparks with characteristic dimension D ∼ h, separated from one another by a distance d ∼ h, where a = r p /h is the complexity parameter (see also Fan et al 2001). Keeping in mind the grazing viewing trajectory in PSR B0943+10, we consider an arrangement of N = 20 < N max sparks on a periphery of the polar cap in this pulsar.…”

Differential frequency-dependent delay from the pulsar magnetosphere

“…The rate of rotation has been measured for a few pulsars, A&A 552, A61 (2013) allowing detailed maps of the polar cap to be made (see for example, Deshpande & Rankin 2001), and modified versions of this model have been used to try to explain all of the features listed above (see e.g. Filippenko & Radhakrishnan 1982;Gil & Sendyk 2000;Gil et al 2003Gil et al , 2008.…”