What can quasi-periodic oscillations tell us about the structure of the corresponding compact objects?
Article first published online: 4 APR 2012
© 2012 The Author. Monthly Notices of the Royal Astronomical Society © 2012 RAS
Monthly Notices of the Royal Astronomical Society
Volume 422, Issue 3, pages 2581–2589, May 2012
How to Cite
Pappas, G. (2012), What can quasi-periodic oscillations tell us about the structure of the corresponding compact objects?. Monthly Notices of the Royal Astronomical Society, 422: 2581–2589. doi: 10.1111/j.1365-2966.2012.20817.x
- Issue published online: 10 MAY 2012
- Article first published online: 4 APR 2012
- Accepted 2012 February 23. Received 2012 February 22; in original form 2011 December 21
- equation of state;
- methods: analytical;
- stars: neutron;
- X-rays: binaries
We show how one can estimate the multipole moments of the space–time, assuming that the quasi-periodic modulations of the X-ray flux (quasi-periodic oscillations), observed from accreting neutron stars or black holes, are due to orbital and precession frequencies (relativistic precession model). The precession frequencies Ωρ and Ωz can be expressed as expansions on the orbital frequency Ω, in which the moments enter the coefficients in a prescribed form. Thus, observations can be fitted to these expressions in order to evaluate the moments. If the compact object is a neutron star, constraints can be imposed on the equation of state. The same analysis can be used for black holes as a test for the validity of the no-hair theorem. Alternatively, instead of fitting for the moments, observations can be matched to frequencies calculated from analytic models that are produced so as to correspond to realistic neutron stars described by various equations of state. Observations can thus be used to constrain the equation of state and possibly other physical parameters (mass, rotation, quadrupole, etc.). Some distinctive features of the frequencies, which become evident by using the analytic models, are discussed.