English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The high-frequency quasi-periodic oscillations (HF QPOs) that appear in theX-ray fluxes of low-mass X-ray binaries remain an unexplained phenomenon. Amongother ideas, it has been suggested that a non-linear resonance between twooscillation modes in an accretion disc orbiting either a black hole or aneutron star plays a role in exciting the observed modulation. Several possibleresonances have been discussed. A particular model assumes resonances in whichthe disc-oscillation modes have the eigenfrequencies equal to the radial andvertical epicyclic frequencies of geodesic orbital motion. This model has beendiscussed for black hole microquasar sources as well as for a group of neutronstar sources. Assuming several neutron (strange) star equations of state andHartle-Thorne geometry of rotating stars, we briefly compare the frequenciesexpected from the model to those observed. Our comparison implies that theinferred neutron star radius "RNS" is larger than the related radius of themarginally stable circular orbit "rms" for nuclear matter equations of stateand spin frequencies up to 800Hz. For the same range of spin and a strange star(MIT) equation of state, the inferrred radius RNS is roughly equal to rms. ThePaczynski modulation mechanism considered within the model requires that RNS <rms. However, we find this condition to be fulfilled only for the strangematter equation of state, masses below one solar mass, and spin frequenciesabove 800Hz. This result most likely falsifies the postulation of the neutronstar 3:2 resonant eigenfrequencies being equal to the frequencies of geodesicradial and vertical epicyclic modes. We suggest that the 3:2 epicyclic modescould stay among the possible choices only if a fairly non-geodesic accretionflow is assumed, or if a different modulation mechanism operates.

Disc-oscillation resonance and neutron star QPOs: 3:2 epicyclic orbital model