The emission positions of kHz QPOs and Kerr spacetime influence
C.M. Zhang, Y.C. Wei, H.X. Yin, Y.H. Zhao, Y.J. Lei, L.M. Song, F., Zhang, Y.Yan
TL;DR
This paper estimates the emission positions of kHz QPOs using models based on Alfven wave oscillations and relativistic precession, analyzing the influence of Kerr spacetime and spin effects on these positions.
Contribution
It introduces a method to estimate kHz QPO emission sites considering Kerr spacetime effects and compares different models for twin kHz QPOs.
Findings
Most kHz QPOs originate at approximately 18 km from the neutron star.
Spin effects in Kerr spacetime modify the QPO frequencies by about 2-5%.
Emission positions vary among different QPO sources, with Cir X-1 at about 30 km.
Abstract
Based the Alfven wave oscillation model (AWOM) and relativistic precession model (RPM) for twin kHz QPOs, we estimate the emission positions of most detected kHz QPOs to be at r=18+-3 km (R/15km) except Cir X-1 at r = 30\+-5 km (R/15km). For the proposed Keplerian frequency as an upper limit to kHz QPO, the spin effects in Kerr Spacetime are discussed, which have about a 5% (2%) modification for that of the Schwarzchild case for the spin frequency of 1000 (400) Hz.The application to the four typical QPO sources, Cir X-1, Sco X-1, SAX J1808.4-3658 and XTE 1807-294, is mentioned.
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