Interpreting QPOs from Accreting Neutron Stars

Abstract

The high time resolution and large area of the Rossi X-ray Timing Explorer have been essential in the detection and characterization of high-frequency quasi-periodic variability in the flux from neutron stars in low-mass X-ray binaries. An unknown phenomenon prior to RXTE, kilohertz quasi-periodic oscillations (QPOs) have now been detected from more than twenty systems. Their high frequencies (up to 1330 Hz) imply that they are generated close to the neutron star, where general relativistic effects are expected to play an important role. I summarize current models for the kilohertz QPO phenomenon. In particular, I show that there is a significant domain of agreement among the models that can be used to constrain neutron star structure and look for signatures of highly curved spacetime in the properties of the QPOs.