Confronting models of twin peak quasiperiodic oscillations: Mass and spin estimates fixed by neutron star equation of state
Abstract
Twinpeak quasiperiodic oscillations (QPOs) are observed in the Xray powerdensity spectra of several accreting lowmass neutron star (NS) binaries. In our work we consider several QPO models and focus especially on the atoll source 4U 163653 with its large set of QPO measurements. We find that the considered models require the QPO excitation radii in 4U 163653 to be close to the innermost stable circular orbit of the accretion disc. We explore and summarize massangularmomentum relations and limits on NS compactness implied by individual QPO models. We confront these relations with NS parameters given by various NS equations of state (EoS). The application of concrete EoS removes the degeneracy in the mass and angular momentum determined from the QPO models when the spin frequency is known. Moreover, the applied NS EoS are compatible only with some of the considered QPO models. In our work we compare simplified calculations that assume Kerr background geometry to the detailed calculations considering NS oblateness influence in HartleThorne spacetimes.
 Publication:

Proceedings of RAGtime 1416: Workshops on black holes and neutron stars
 Pub Date:
 December 2014
 Bibcode:
 2014bhns.work..269T
 Keywords:

 Xrays: binaries;
 Accretion;
 accretion disks;
 Stars: neutron;
 Equation of state