Frequency evolution of pulsar emission: Further evidence for fan beam model

Abstract

Aims. We explore frequency-dependent changes in pulsar radio emission by analyzing their profile widths and emission heights, assessing whether the simple radius-to-frequency mapping (RFM) or the fan beam model can describe the data. Methods. Using wideband (704-4032 MHz) Murriyang (Parkes) observations of over 100 pulsars, we measured profile widths at multiple intensity levels, fit Gaussian components, and used aberration-retardation effects to estimate emission altitudes. We compared trends in width evolution and emission height with a fan beam model. Results. Similar to other recent studies, we find that while many pulsars show profiles narrowing with increasing frequency, a substantial fraction show the reverse. The Gaussian decomposition of the profiles reveals that the peak locations of the components vary little with frequency. However, the component widths do, in general, narrow with increasing frequency. This argues that propagation effects are responsible for the width evolution of the profiles rather than emission height. Overall, the evolution of the emission height with frequency is unclear, and clouded by the assumptions in the model. Spin-down luminosity correlates weakly with profile narrowing but not with emission height. Conclusions. The classic picture where pulsars emit at a single emission height which decreases with increasing observing frequency cannot explain the diversity in behavior observed here. Instead, pulsar beams likely originate from extended regions at multiple altitudes, with fan-beam or patchy structures dominating their frequency evolution. Future models must incorporate realistic plasma physics and multi-altitude emission to capture the range of pulsar behaviors.

References in corpus (19)

• Profile and polarization characteristics of energetic pulsars
• Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations
• An empirical model for the beams of radio pulsars
• Profile morphology and polarization of young pulsars
• Direct Observations of Tether-cutting Reconnection During a Major Solar Event From 2014 February 24 to 25
• Constraints on viewing geometries from radio observations of $\gamma$-ray-loud pulsars using a novel method
• A Fan Beam Model for Radio Pulsars. I. Observational Evidence
• The Thousand-Pulsar-Array programme on MeerKAT XI: Application of the rotating vector model
• The Thousand-Pulsar-Array program on MeerKAT -- IX. The time-averaged properties of the observed pulsar population
• The Thousand-Pulsar-Array programme on MeerKAT: -- VI. Pulse widths of a large and diverse sample of radio pulsars
• On the difference between gamma-ray-detected and non-gamma-ray-detected pulsars
• Mapping the magnetosphere of PSR B1055-52
• Two years of pulsar observations with the Ultra-Wideband Receiver on the Parkes radio telescope
• A polarization census of bright pulsars using the Ultra-Wideband Receiver on the Parkes radio telescope
• The origin of the frequency-dependent behaviour of pulsar radio profiles
• Pulsar polarization: a broad-band population view with the Parkes Ultra-Wideband receiver
• New pulse profile variability associated with a glitch of PSR J0738-4042
• Rotational and radio emission properties of PSR J0738-4042 over half a century
• Role of Fan Beam Model in Population Synthesis of Isolated Radio Pulsars