Modeling the frequency-dependence of radio beams for cone-dominant pulsars

TL;DR

This paper models the frequency dependence of radio beam radii in cone-dominant pulsars using curvature radiation, showing that two density patches with energy loss explain observed power-law relations.

Contribution

It introduces a numerical simulation approach considering particle density and energy distributions to explain the frequency dependence of pulsar beam radii.

Findings

Simulated profiles with two density patches produce power-law indices consistent with observations.

Energy distributions and radial energy decay significantly influence the frequency dependence behavior.

Proper beam radius behavior requires models with radial energy loss of particles.

Abstract

Beam radii for cone-dominant pulsars follow a power-law relation with frequency, $\vartheta = (\nu/\nu_0)^k+\vartheta_0$, which has not yet well explained in previous works. We study this frequency dependence of beam radius (FDB) for cone-dominant pulsars by using the curvature radiation mechanism. Considering various density and energy distributions of particles in the pulsar open field line region, we numerically simulate the emission intensity distribution across emission height and rotation phase, and get integrated profiles at different frequencies and obtain the FDB curves. For the density model of a conal-like distribution, the simulated profiles always shrink to one component at high frequencies. In the density model with two separated density patches, the profiles always have two distinct components, and the power-law indices $k$ are found to be in the range from -0.1 to -2.5, consistent with observational results. Energy distributions of streaming particles have significant influence on the frequency-dependence behavior. Radial energy decay of particles are necessary to get proper $\vartheta_0$ in models. We conclude that by using the curvature radiation mechanism, the observed frequency dependence of beam radius for the cone-dominant pulsars can only be explained by the emission model of particles in two density patches with a Gaussian energy distribution and a radial energy loss.