Open Access Dissertation
Date of Award
Physics and Astronomy
Kilohertz quasi-periodic oscillations or kHz QPOs are X-ray intensity variations observed
in neutron star low-mass X-ray binary (LMXB) systems. In such systems, matter is transferred
from a secondary low-mass star to a neutron star via the process of accretion. kHz
QPOs occur on the timescale of the inner accretion flow and may carry signatures of the
physics of strong gravity (c2 ~GM/R) and possibly clues to constraining the neutron star
equation of state (EOS). No model to date has been able to illuminate the origin of kHz
QPOs. Spectral-timing is a set of analysis techniques useful in deriving information about
the nature of physical processes occurring within the accretion flow on the timescale of the
kHz QPO. We present a comprehensive study of spectral-timing products of kHz QPOs from
systems where data is available in NASA’s Rossi X-ray Timing Explorer (RXTE) archive to
demonstrate the promise of these techniques and to gain insights regarding the origin of kHz
QPOs. Using data averaged over the entire RXTE archive, we show correlated time-lags
as a function of QPO frequency and energy, as well as energy-dependent covariance spectra
for the various LMXB systems where spectral-timing analysis is possible. The similarity in
trends in all sources suggest a common physical origin for kHz QPOs across the population.
The diferences in results between lower and upper kHz QPOs lend further support to the
evidence of the differing nature of the lower and upper kHz QPOs.
Troyer, Jon, "Spectral–timing Analysis Of Kilohertz Quasi–periodic Oscillations In Neutron Star Low Mass X-Ray Binaries" (2018). Wayne State University Dissertations. 1972.