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

We present results of a combined investigation of the spectral and kHz QPOevolution around the Z-track in GX 5-1 based on high-quality RXTE data. TheExtended ADC emission model provides very good fits to the spectra, the resultspointing clearly to a model for the nature of the Z-track, in agreement withprevious results for the similar source GX 340+0. In this model, at the softapex of the Z-track, the mass accretion rate Mdot is minimum and the neutronstar has its lowest temperature; but as the source moves along the normalbranch, the luminosity of the Comptonized emission increases, indicating thatMdot increases and the neutron star gets hotter. The measured flux f of theneutron star emission increases by a factor of ten becoming super-Eddington,and we propose that this disrupts the inner disk so forming jets. In flaring,the luminosity of the dominant Comptonized emission from the ADC is constant,while the neutron star emission increases, and we propose for the first timethat flaring consists of unstable nuclear burning on the neutron star, and themeasured mass accretion rate per unit area mdot at the onset of flaring agreeswell with the theoretical critical value at which burning becomes unstable.There is a striking correlation between the frequencies of the kHz QPO and theratio of the flux to the Eddington value: f/f_Edd, suggesting an explanation ofthe higher frequency QPO and of its variation along the Z-track. It is wellknown that a Keplerian orbit in the disk at this frequency corresponds to aposition some distance from the neutron star; we propose that the oscillationalways occurs at the inner disk edge, which moves radially outwards on theupper normal and horizontal branches as the measured increasing radiationpressure increasingly disrupts the inner disk.

A model for the Z-track phenomenon in GX 5-1 and observational evidence for the physical origins of the kHz QPO