Rutgers University Astrophysics Seminar

Abstract: The talk will be divided mainly into two parts; the first part will discuss the orbital evolution and apsidal motion of a few X-ray binary pulsars and the second part will discuss the long term superorbital studies (mainly about Cen X-3 aperiodic intensity variations). The orbital evolution of few high mass X-ray binaries will be presented. Tidal interaction, mass loss from the binary system and mass transfer from the normal companion star to the neutron star all contribute to orbital evolution. Orbits of some X-ray binaries which are eccentric also allow for measuring the rate of apsidal motion of the binary orbit. Measuring the rate of apsidal motion allows one to estimate the apsidal motion constant of the companion star which in turn can be a test for stellar structure models. The results of these studies will be presented. Cen X-3 shows aperiodic long term intensity variations with timescales of a few days to a hundred days. This is in contrast to the superorbital intensity variations observed in other X-ray binary pulsar systems that are periodic (Her X-1, LMC X-4) or quasi-periodic (SMC X-1) and understood to occur due to obscurtion of the central X-ray source by a warped or inclined precesing accretion disk. The Cen X-3 QPOs, orbital modulation and the pulsed fraction measurements in different source intensity states provide clues to understanding the aperiodic intensity variations. The results of these studies will be discussed in the talk.