Search for coherent X-Ray pulsations from neutron stars in low mass X-Ray binaries using rossi X-Ray timing explorer observations

Official URL: https://risc01.sabanciuniv.edu/record=b2486340 _(Table of contents)

Low mass X-ray binaries (LMXBs) are binary systems that emit luminous X-rays mainly by converting the gravitational energy of the matter from a low mass (M .1 M ) star into radiation as it accretes onto a neutron star or a black hole. Only a small fraction of LMXBs show coherent pulsations during their persistent emission phase. The cause of the lack of pulsations is still unclear. Detection of intermittent pulsations from a few LMXBs promise a better understanding of the physical mechanism causing the absence of pulsations. In this thesis, we present the results of our extensive search for pulsations in 13 LMXBs after binary orbital motion correction. These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1122 Hz, and have a binary orbital period varying from 2.1 to 18.9 hours. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer (RXTE) data of these sources. Then, we applied binary orbital corrections to these pulsation episodes to discard the smearing effect of the binary orbital motion and searched for recovered pulsations at the second stage. Here we report 75 pulsation episodes that contain weak but coherent pulsations around the burst oscillation frequency. Furthermore, we report eight new episodes that show relatively strong pulsations in the binary orbital motion corrected data. We also present results of our two sets of simulations: one is to understand the effects of orbital binary motion to the pulse detection and the other one is to find the relation between pulsed the fractional amplitude and source intensity