Radiation mechanism of twin kilohertz quasi-periodic oscillations in neutron star low mass X-ray binaries

TL;DR

This paper proposes a self-consistent radiation mechanism model for twin kHz QPOs in neutron star X-ray binaries, linking MHD wave disturbances to observed oscillations and matching observational data with theoretical predictions.

Contribution

It introduces a novel model connecting twin MHD waves to twin kHz QPOs and validates it with observational data from 4U 1636--53.

Findings

Electron temperature decreases with seed photon temperature.

A tight exponential relation between flux and seed photon temperature.

Model successfully explains twin kHz QPO origin through MHD wave disturbances.

Abstract

Context: The connection between quasi-periodic oscillations (QPOs) and magnetic fields has been investigated across various celestial bodies. Magnetohydrodynamics (MHD) waves have been employed to explain the simultaneous upper and lower kilohertz (kHz) QPOs. Nevertheless, the intricate and undefined formation pathways of twin kHz QPOs present a compelling avenue for exploration. This area of study holds great interest as it provides an opportunity to derive crucial parameters related to compact stars. Aims:We strives to develop a self-consistent model elucidating the radiation mechanism of twin kHz QPOs, subsequently comparing it with observations. Methods: A sample of 28 twin kHz QPOs observed from the X-ray binary 4U 1636--53 are used to compare with the results of the MCMC calculations according to our model of the radiation mechanism of twin kHz QPOs, which is related to twin MHD waves. Results: We obtain twenty-eight groups of parameters of 4U 1636--53 and a tight exponential fit between the flux and the temperature of seed photons to Compton up-scattering and find that the electron temperature in the corona around the neutron star decreases with the increasing temperature of the seed photons. Conclusions: The origin of twin kHz QPOs can be attributed to dual disturbances arising from twin MHD waves generated at the innermost radius of an accretion disc. The seed photons can be transported through a high temperature corona and Compton up-scattered. The variability of the photons with the frequencies of twin MHD waves can lead to the observed twin kHz QPOs.