Simulation of the distribution of radio pulsar nulling fractions

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi, Xinjiang 830011, China
² Xinjiang Key laboratory of Radio Astrophysics, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi, Xinjiang 830011, China
³ Key Laboratory of Radio Astronomy and Technology (Chinese Academy of Sciences), A20 Datun Road, Chaoyang District, Beijing 100101, PR China
⁴ SIfA, School of Physics, University of Sydney, Sydney, NSW 2006, Australia

^⋆ Corresponding author: ryuen@xao.ac.cn

Received: 20 January 2025
Accepted: 9 April 2025

Abstract

Aims. In this work, we aim to simulate the observed distribution of the pulse nulling fractions (NFs) in radio pulsars and to investigate the associated properties of the emission region.

Methods. We identified three conditions related to the occurrence of pulse nulling. From the traditional approach for correlation of the pulsed radio intensity and plasma density, a pulse cessation results from switching in the plasma density to zero. Second, recent observations have shown that the occurrence of a pulse cessation appears to favor certain emission conditions. Third, the observation of specific emission properties across different parts of a profile indicates that the emission region may be segmented. A detectable null would then correspond to the presence of a favorable condition, whereby the switching to zero plasma density occurs in all the emission segments visible to the observer. By dividing the emission region into equal segments around the magnetic axis, we simulated the distribution of NFs based on 5000 pulsar samples, each with 1000 rotations.

Results. Our results show that an emission region with 16 ± 4 segments gives the best-fit NF distribution for the recent observations. We find that while the number of nulling pulsars increases as their age increases, the NFs do not demonstrate a strong correlation with the obliquity angle, measured between the rotation and the magnetic axes. We show that the former relationship is related to the emission geometry, whereas the latter may be due to an additional mechanism on top of the traditional radio emission generation. The model predicts that nulling is expected to occur in all pulsars, although it is more common in pulsars of older ages.