A model for double notches and bifurcated components in radio profiles of pulsars and magnetars. Evidence for the parallel acceleration maser in pulsar magnetosphere

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 nu_obs roughly at a rate Delta� nu_obs^-1/2, where Delta 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. Appendices are only available in electronic form at http://www.aanda.org