1201.6071 (George Pappas)

What can QPOs tell us about the structure of the corresponding compact
objects?    [PDF]

George Pappas

We show how one can estimate the multipole moments of the space-time,
assuming that the quasi-periodic modulations of the X-ray flux (QPOs), observed
from accreting neutron stars or black holes, are due to orbital and precession
frequencies (relativistic precession model). The precession frequencies
$\Omega_{\rho}$ and $\Omega_z$ can be expressed as expansions on the orbital
frequency $\Omega$, in which the moments enter the coefficients in a prescribed
form. Thus observations can be fitted to these expression to evaluate the
moments. If the compact object is a neutron star, constrains 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, that
become evident by using the analytic models, are discussed.

View original: http://arxiv.org/abs/1201.6071