Study Of The Millihertz Quasi-periodic Oscillations In Low-mass X-ray Binaries

The millihertz quasi-periodic oscillations(m Hz QPOs)in low mass X-ray binaries are supposed to originate from a marginally stable nuclear burning of helium on the neutron surface.Therefore,the study of the m Hz QPOs is important to deeply understand the progress of nuclear burning on the neutron surface.At present,many observations with m Hz QPOs have been accumulated.In this work,we analyzed the m Hz QPOs and their second harmonic component in two neutron-star low-mass X-ray binaries to study the observational characteristics of the m Hz QPOs.In this thesis,we firstly studied the second harmonic component of the m Hz QPOs in 4U 1636-53 based on the data from RXTE satellite.We found that the harmonics of the m Hz QPOs most likely appear in the transitional spectral state of the binary system.In addition,the ratio of the rms amplitude of the harmonic component to the rms amplitude of the fundamental component is constant,?0.6.The energy distribution of the rms amplitude of the harmonic component is consistent with that of the fundamental component.Finally,we found that the harmonic component do not always exist,and only 40% of the m Hz QPOs show harmonic components.In addition,we have detected a significant m Hz QPO and its harmonic in another binary system 4U 1608-52 observed by the NICER detector.We analyzed the rms amplitude of the m Hz QPO,and found that the distribution of their rms amplitude vs energy is consistent with the rms-energy relation reported in 4U 1636-53.This indicates that the rms-energy relation may be a common feature of the m Hz QPOs from neutron-star surface.The structure of this paper is as follow: In the first chapter,we introduce some related background: the classification and the features of the binary systems,the structure and the parameters of the neutron stars.The second chapter is about the classification of QPOs and their features.In the third chapter we introduce the research methods and tools used for the analysis of the m Hz QPO in neutron star low mass Xray binaries.We put the result of the analysis of m Hz QPOs in 4U 1636-53 in chapter4.The last chapter is about the detection and analysis of the m Hz QPO in 4U 1608-52 by the NICER detector.