Common patterns in pulse profiles of High Mass X-ray Binaries

TL;DR

This study classifies energy-resolved pulse profiles of high-mass X-ray binary pulsars, revealing clear categories but no strong correlation with system parameters, suggesting other hidden factors influence pulse profile shapes.

Contribution

We developed a classification method for X-ray pulsar pulse profiles based on Fourier analysis, providing a new framework to analyze their energy-dependent behavior.

Findings

Pulse profiles can be categorized into three groups based on shape and harmonic dominance.

No conclusive correlation found between pulse profile groups and system parameters.

A weak trend suggests a possible link between pulse profile classification and spin-orbital period relation.

Abstract

The pulsations of X-ray pulsars carry information about the accretion and magnetic field geometry. Here we present a study and classification of energy resolved pulse profiles of a sample of X-ray pulsars, focusing on high-mass X-ray binaries. Our goal is to perform a classification of X-ray pulsars based on their observed pulse profiles and look for correlations between this classification and their principle physical observables. The analysis pipeline is available online. We analysed the pulse profiles of a sample of X-ray pulsars using data obtained with the XMM-Newton and NuSTAR. We fit the energy resolved pulse profiles with a Fourier series of up to five harmonics. We investigate relationships between the pulse profile properties and other observables of the systems (e.g., orbital period, magnetic field strength, and luminosity) to study the extreme physics of these systems. The sources were divided into three groups by a classification based on the shape, the dominance of the fitted Fourier harmonics and their respective evolution with energy. We do not find a conclusive correlation between the pulse profile shapes or groups and other parameters of the systems. However, a weak trend was found when comparing our classification to the sources' location in the spin period-orbital period diagram. Further studies are required to confirm this trend. Despite the large variety of pulse profiles of the X-ray pulsars, we found that with our approach clear categories emerge which we use to classify their behavior as function of energy. As we do not find a clear relationship between our classification scheme and other parameters we conclude that X-ray pulse profiles are influenced by other hidden variables.