Revisiting the shape of radio emission beam from pulsars

ABSTRACT The shape of the interpulse emission beam of PSR J1906+0746 cannot be described by the current conal beam and fan beam models. To address this issue, this paper presents a modified fan beam model based on the model proposed by Wang et al. (hereafter WPZ14 model). The modified model retains the concept of the flux tube in the outer part of the emission beam from the WPZ14 model. However, it improves the description of the shape of the inner part of the emission beam by including the characteristics of the interpulse beam of PSR J1906+0746. Within a suitable parameter space, the modified model can adequately describe the positive statistical correlation between the 10 per cent pulse width and the absolute value of the impact angle for 210 normal pulsars (i.e. non-millisecond pulsars). Within this derived parameter space, the emission beams exhibit a typical feature of lateral compression, indicating that the polar caps of many pulsars are underfilled with emission. Possible physical implications are discussed.