A model for double notches and bifurcated components in radio profiles of pulsars and magnetars

Abstract

Context. Averaged pulse profiles of three nearby pulsars: B1929+10, J0437−4715 and B0950+08 exhibit unusual "double notches". These W-like looking features consist of two adjacent V-shaped dips that approach each other at increasing observation frequency ν obs roughly at a rate ∆ ∝ ν −1/2 obs , where ∆ is the separation between the notches' minima. Aims. We show that basic properties of the notches, namely their W-like look and the rate of their converging can be understood within a narrow class of models of coherent radio emission from pulsars: the free electron maser models based on coherent inverse Compton scattering of parallel oscillations of ambient electric field. Methods. The observed properties of the pulsars imply that the Fourier spectrum of the wiggler-like oscillations is narrow and that the broad-band character of the radio emission reflects the width of the electron energy distribution.Results. Such a model provides a natural explanation for the frequency-independent separation between the main pulse and interpulse of B0950+08 as well as for the lack of radius to frequency mapping in the conal-like emission of J0437−4715. The frequency behaviour of the main pulse in the profile of the first radio magnetar XTE J1810−197 can also be explained within this model.

Timing, polarimetry and physics of the bright, nearby millisecond pulsar PSR J0437−4715 – a single-pulse perspective

“…Strong deviations from log-normality approaching a power law distribution are visible, with a significant population of pulses with very high magnitudes. We note that the flux density distribution in the notches, i.e., the "w" shaped feature (see e.g., Dyks et al 2007) of the average pulse profile visible around phase 0.7 of Fig. 1, is indistinguishable from the distribution in nearby phases.…”

“…The association of OPMs with highly modulated emission has been first noted by McKinnon (2004) and explained statistically by van Straten (2009). Furthermore, Dyks et al (2007Dyks et al ( , 2010 argue that PSR J0437−4715 is likely to exhibit OPMs and that the trailing side of the pulse profile is dominated by the extraordinary polarisation mode, as this mode can explain the creation of the notches by assuming curvature emission from thin plasma streams. We note that soliton emission seen only in the leading part of the profile is also expected to result in the extraordinary mode.…”

Polarization observations of 20 millisecond pulsars

“…There are multiple overlapping components, and the present results show that the pulse profile extends over at least 85 per cent of the pulse period. The notches in Stokes I and L discussed by Navarro et al (1997) and Dyks, Rudak & Rankin (2007) are clearly visible in the central expanded plot. The observed PA variations cannot be described by the RVM, even if orthogonal mode jumps are taken into account.…”

A Broadband Radio Study of the Average Profile and Giant Pulses From PSR B1821-24a

“…in the pulsar magnetosphere (Wright 2004) or a representation of the shape of a microscopic beam of emitted coherent radiation (Dyks et al 2007;Dyks & Rudak 2012). We compared the properties of M28A's dips with the properties of double notches in the literature.…”