Investigation of temporal variability in black hole and neutron star binary systems across different timescales

Abstract

X-ray binary (XRB) systems, comprising a stellar remnant (neutron star or black hole) and a companion star, are key objects for studying accretion physics and the extreme conditions, such as intense gravity and magnetic fields, around compact objects. These X-ray binary systems sometimes showhigh periodic variabilities on the scales ranging from a fewseconds to some days. The periodicity at the scales of milliseconds to seconds can be the pulsation of the neutron star, at the scales of a few hours or days can be the orbital period, and the scales longer than the orbital period are super-orbital periodicities, which arise due to different mechanisms going on there in the accretion disk. This project deals with the analysis of XRBs, focusing on detecting periodicities and understanding the physical processes giving rise to them. Using techniques such as the Lomb-Scargle periodogram for unevenly sampled data, rescaling of the power spectrum to get the noise continuum to remove the red noise component present in the power spectrum, and false alarm probability (FAP) calculations are used to get the significant periodicities in these systems. The science cases of pulsations and super-orbital periods explored to probe neutron star spin and the accretion disk behavior, respectively. This project focuses on the importance of noise reduction techniques in extracting meaningful periodic signals and further enhancing our understanding of compact objects and accretion disk behavior in XRBs. In addition, it focuses on the study of long-term evolution of detected periodicities to get the ideas about the evolving mechanisms producing them and the energy dependence of the superorbital periodicities to get an idea about the emitting region from the system. Other than superorbital periods, we also conducted an analysis to investigate the temporal evolution of pulsation in selected XRBs. Also, an effort is made to model eclipses in these systems which can give a deeper insights of XRBs.