The Observational Study Of The Accreting X-ray Pulsars

In this paper,the radiation characteristics of accreting X-ray pulsars are intro-duced.We used the observations from Insight-HXMT,the first X-ray satellite launched by China in 2017,to study the timing and spectral properties of X-ray binaries under the strong magnetic field and gravity,including the evolution of the spin period and pulse profiles in a neutron star,the binary orbital parameters,the quasi-periodic oscil-lation（QPO）,and the cyclotron absorption lines,to understand the accretion physics and high-energy radiation mechanism of neutron stars.Accreting X-ray binary pulsars（XRBPs）,first discovered with the Uhuru satellite[1],are comprised of a highly magnetized neutron star（NS）and an optical companion star,which provides an individual laboratory for understanding the accretion process and radiation characteristics in a strong magnetic field(higher than 10¹²G)and a strong gravitational field.Since their discovery,XRBPs have been extensively studied in X-ray astronomy.For example,in the strong magnetic field,the cyclotron absorption lines also named CRSFs in energy spectrum were seen in most of the XRBPs[2].And the local magnetic strength of neutron stars can be directly measured because the CRSF energy is related to the magnetic field in the line-forming region.In addition,the dependence of CRSF energies on luminosity could be associated with the different accretion regimes[3–5],and could help us to analyze the accretion geometry,accretion column structure and so on.In addition to the study of the spectral features,the timing behavior is also in-cluded.The change of pulse period can help us understand the mass transfer mechanism,and the shape of the pulse profiles can be associated with the emission angle（such as the fan beam or pencil beam[6]）.And measure the orbital parameters of the binary system accurately by temporal analysis.We also study the quasi-periodic oscillation（QPO）and its unknown physical origin.In Chapter 3,the cyclotron absorption line of pulsar binary Vela X-1 is studied.The energies of the two cyclotron lines are 21-27 ke V and 43-50 ke V respectively.The positive correlation between the fundamental cyclotron energy and luminosity indicates the change of radiation height of the accretion column height,which implies that it may be in a sub-critical accretion regime.There may be a negative correlation at lower luminosity.Long-term significant variations of the absorption column density and its evolution over the pulse phase may imply the existence of the clumpy wind structure near the neutron star.Chapter 4 to 6 is the study of accretion pulsar Cen X-3.The quasi-periodic oscil-lation characteristics in 40 m Hz of Cen X-3 are studied,including the discussion of the physical origin of QPO.We study the variations of the cyclotron absorption line in Cen X-3 over luminosity,pulse phase,and orbital phase.We also investigate the evolution of the pulse profile of Cen X-3 with energy and time,the results show that the emis-sion pattern may transition from a mixture of a pencil and a fan beam to a dominated pencil-like.The spin period and orbital parameters of Cen X-1 are accurately measured by binary orbital fitting.