Kilohertz QPOs in low-mass X-ray binaries as oscillation modes of tori around neutron stars - I

Author(s)

de Avellar, Marcio G. B. ^{[1, 2]} ; Porth, Oliver ^[2] ; Younsi, Ziri ^[2] ; Rezzolla, Luciano ^{[2, 3]}

Affiliation

^[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, BR-05508090 Sao Paulo - Brazil

^[2] Goethe Univ Frankfurt, Inst Theoret Phys, Max von Laue Str 1, D-60438 Frankfurt - Germany

^[3] Frankfurt Inst Adv Studies, Ruth Moufang Str 1, D-60438 Frankfurt - Germany

• Document type: Journal article
• Source: Monthly Notices of the Royal Astronomical Society; v. 474, n. 3, p. 3967-3975, MAR 2018.
• Web of Science Citations: 7

Abstract

There have been many efforts to explain the dynamical mechanisms behind the phenomenology of quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries. Up to now, none of the models can successfully explain all the frequencies observed in the power spectral density of the light curves. After performing several general-relativistic hydrodynamic simulations of non-self-gravitating axisymmetric thick tori with constant specific angular momentum oscillating around a neutron star such as the one associated with the low-mass X-ray binary 4U 1636 - 53, we find that the oscillation modes give rise to QPOs similar to those seen in the observational data. In particular, when matching pairs of kilohertz QPOs from the numerical simulations with those observed, certain combinations reproduce well the observations, provided we take a mass for the neutron star that is smaller than what is generally assumed. At the same time, we find that tori with constant specific angular momentum cannot match the entire range of frequencies observed for 4U 1636-53 due to physical constraints set on their size. Finally, we show that our results are consistent with the observed shifts in QPO frequency that could accompany state transitions of the accretion disc. (AU)

• FAPESP's process: 13/26258-4 - Superdense matter in the universe
• Grantee: Manuel Máximo Bastos Malheiro de Oliveira
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 15/20553-0 - Modelling the Quasi-Periodic Oscillations and Their Respective Time Lags in Neutron Star Low-Mass X-Ray Binaries - The NS-LMXB 4U 1636-53 as a case study
• Grantee: Marcio Guilherme Bronzato de Avellar
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor