Düşük Manyetik Alana Sahip Nötron Yıldızları Çevresindeki Diskler

Abstract

This study deals with accretion disks around weakly magnetized neutron stars. In this work we aim to come up with possible explanations for observational phenomena within a physically plausible model by studying accretion disks around weakly magnetized neutron stars. Investigating accretion disks around weakly magnetized neutron stars is important for studying and understanding the physics of neutron stars. Under reasonable assumptions and physical constraints, accretion disks can be examined using two different regimes: Gas pressure dominated or radiation pressure dominated. In this thesis, zeroth order disk solutions which were also obtained in the early 70's (Shakura ve Sunyaev, 1973) are employed while taking into account the existence of a non-Keplerian boundary layer in the innermost region of the disk and unified disk solutions are found. Boundary layers which define the innermost disk boundary condition for physically plausible unified disk solutions are used to explain the correlation between kHz quasi-periodic oscillation (QPO) frequencies observed in neutron star low-mass X-ray binaries and the X-ray flux in accordance with the Boundary Region Model (BRM) (Alpar ve Psaltis, 2008; Erkut et al., 2008). This study has revealed that the parallel tracks phenomena observed with long timescales for the correlation between kHz QPO frequencies and the X-ray flux of the neutron stars in low-mass X-ray binaries can be explained within the frame of the BRM under plausible assumptions and self-consistent physical constraints. The model data obtained in this thesis can be used in a subsequent work to determine the masses, radii and magnetic field strengths of the neutron stars in LMXB systems we studied.