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Mechanical model of a boundary layer for the parallel tracks of kilohertz quasi-periodic oscillations in accreting neutron stars




TekijätAbolmasov Pavel, Poutanen Juri

KustantajaEDP SCIENCES S A

Julkaisuvuosi2021

JournalAstronomy and Astrophysics

Tietokannassa oleva lehden nimiASTRONOMY & ASTROPHYSICS

Lehden akronyymiASTRON ASTROPHYS

Artikkelin numeroARTN A45

Vuosikerta647

Sivujen määrä7

ISSN0004-6361

eISSN1432-0746

DOIhttps://doi.org/10.1051/0004-6361/202039485

Rinnakkaistallenteen osoitehttps://research.utu.fi/converis/portal/detail/Publication/53707718


Tiivistelmä
Kilohertz-scale quasi-periodic oscillations (kHz QPOs) are a distinct feature of the variability of neutron star low-mass X-ray binaries. Among all the variability modes, they are especially interesting as a probe for the innermost parts of the accretion flow, including the accretion boundary layer (BL) on the surface of the neutron star. All the existing models of kHz QPOs explain only part of their rich phenomenology. Here, we show that some of their properties can be explained by a very simple model of the BL that is spun up by accreting rapidly rotating matter from the disk and spun down by the interaction with the neutron star. In particular, if the characteristic time scales for the mass and the angular momentum transfer from the BL to the star are of the same order of magnitude, our model naturally reproduces the so-called parallel tracks effect, where the QPO frequency is correlated with luminosity at time scales of hours but becomes uncorrelated at time scales of days. The closeness of the two time scales responsible for mass and angular momentum exchange between the BL and the star is an expected outcome of the radial structure of the BL.

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