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

Black hole and neutron star X-ray binary systems (XRBs) sometimes show high periodic variabilities on scales ranging from a few seconds to days. These are pulsation of the neutron star, orbital period, and superorbital periodicities. The superorbital periodicities, ranging from a few days to hundreds of days, can be attributed to various physical processes in the accretion disk and/or in the binary system. These mechanisms include the precession of the accretion disk, magnetic and radiation-induced wrapping, change in X-ray state, precession of relativistic jets, or the presence of a third body in the system. In this study, we report the long-term variability behavior of XRBs, focusing on detecting periodicities and understanding the physical processes that cause them. We investigated the long-term light curves of a selected sample of 22 black hole and neutron star XRBs employing the Lomb-Scargle periodogram technique using 15 years of data from the MAXI satellite. We examined various methods to address the presence of colored noise in the periodogram and conducted a detailed analysis to rescale the periodogram comprising the red noise to white noise power distribution. Subsequently, we search for significant periodicities in the rescaled periodogram that crosses our threshold criterion, considering the corresponding false alarm probabilities (FAP). We report the detection of both previously reported and newly observed periodicities for a certain subset of sources in our sample. We are focusing 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. We are also examining the temporal evolution (using dynamic periodogram) and energy dependence (using energy-resolved periodograms) of the detected periodicities to reveal the variations in the physical scenarios triggering them and to figure out the regions producing them, respectively. We further expand our analysis to examine the characteristics of long-term behavior of XRBs using alternate widefield telescopes such as Scanning Sky Monitor (SSM) onboard AstroSat. We further aim to study the evolution of complementary timing behavior like pulsation and eclipses over extended timescales. This study, therefore, probes the long-term behavior of XRBs to aid a better understanding of the accretion disk behavior, the pulsation of the neutron star, and the evolution of the binary system.