Statistical Analysis for the Q-factor of twin kHz QPOs

TL;DR

This study statistically analyzes the quality factors of twin kHz QPOs in neutron star LMXBs, revealing distinct distributions and a positive correlation between quality factor and peak frequency, with implications for understanding neutron star accretion.

Contribution

It provides a comprehensive statistical comparison of Q-factor profiles between Z and Atoll sources and explores their relation to peak frequencies using multiple fitting models.

Findings

Quality factors of upper kHz QPOs are narrowly distributed around 8 (Z) and 10 (Atoll).

Lower QPOs show broader distribution with peaks at 5.25 (Z) and 86.22 (Atoll).

Quality factors increase with peak frequency for both upper and lower QPOs.

Abstract

Using the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron star low-mass X-ray binaries (LMXBs), we study the different profiles between bright Z sources and less luminous Atoll sources in a statistical way. We find the quality factors of upper kHz QPOs show a narrow distribution both for Z sources and Atoll sources, which concentrate at 7.98 and 9.75 respectively, the quality factors of lower kHz QPOs show a narrow distribution for Z sources and a broader distribution for Atoll sources, which concentrate at 5.25 and 86.22 respectively. In order to investigate the relation between the quality factor and the peakfrequency of kHz QPOs, we fit the data with power-law, linear and exponential functions, respectively. There is an obvious trend that the quality factors increase with the peak frequencies both for upper and lower QPOs. The implications of our results are discussed.