Meterwavelength Single-pulse Polarimetric Emission Survey. IV. The Period Dependence of Component Widths of Pulsars

Abstract

The core component width in normal pulsars, with periods (P ) > 0.1 seconds, measured at the half-power point at 1 GHz has a lower boundary line (LBL) which closely follows the P −0.5 scaling relation. This result is of fundamental importance for understanding the emission process and requires extended studies over a wider frequency range. In this paper we have carried out a detailed study of the profile component widths of 123 normal pulsars observed in the Meterwavelength Single-pulse Polarimetric Emission Survey at 333 and 618 MHz. The components in the pulse profile were separated into core and conal classes. We found that at both frequencies the core as well as the conal component widths versus period had a LBL which followed the P −0.5 relation with a similar lower boundary. The radio emission in normal pulsars have been observationally shown to arise from a narrow range of heights around a few hundred kilometers above the stellar surface. In the past the P −0.5 relation has been considered as evidence for emission arising from last open dipolar magnetic field lines. We show that the P −0.5 dependence only holds if the trailing and leading half-power points of the component are associated with the last open field line. In such a scenario we do not find any physical motivation which can explain the P −0.5 dependence for both core and conal components as evidence for dipolar geometry in normal pulsars. We believe the period dependence is a result of an yet unexplained physical phenomenon.

Constraining millisecond pulsar geometry using time-aligned radio and gamma-ray pulse profile

“…The emission arises from regions of open dipolar magnetic field lines below 10% of the light-cylinder radius; see Mitra & Li (2004) and Mitra (2017). These conclusions were based on demonstrations that the observed opening angle of normal pulsars follows the P −0.5 (where P is the pulsar period) behaviour (see, e.g., Skrzypczak et al 2018) which is as expected from emission arising from the open dipolar magnetic field line region. Secondly, the polarisation position angle (PPA) across the pulse profile follows the rotating vector model (RVM), which is an indication of emission arising from regions of diverging magnetic field line geometry.…”

Subpulse drifting, nulling, and mode changing in PSR J2006 − 0807 with core emission

“…It has been shown that in pulsars with a central core component, α is related to the core width, sinα = W b P −0.5 /W c , where W c is the core width measured at 50% level of peak intensity, and W b corresponds to the lower boundary of the distribution of the core widths with period (Rankin 1990). The core boundary width have recently been measured to be W b = 2.39±0.26 • , at 333 MHz, by Skrzypczak et al (2018). The angles α and β can also be estimated from the RVM fits to the PPA.…”

“…The emission beam comprises of a central core component, surrounded by nested rings of conal emission (Rankin 1993;Mitra & Deshpande 1999;Mitra & Rankin 2002). Recent studies have shown the core and conal components to originate from similar emission heights (Maciesiak et al 2012;Skrzypczak et al 2018). The shape of the average profile depends on the line of sight (LOS) traverse of the emission beam.…”

Spectral variation across Pulsar Profile due to Coherent Curvature Radiation

“…Table 1 summarises the classification scheme of the pulsar profile types. It has also been shown that the distribution of both the core and the conal component widths with period has similar lower boundary lines which is proportional to P −0.5 (Maciesiak et al 2012;Skrzypczak et al 2018), Core-Cone 2 Center suggesting similar emission heights for both. The pulsar emission is usually highly polarized and shows a polarization position angle (PPA) swing across the profile that resemble a S-shape curve.…”