Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasiperiodic oscillations

Germanà, C.; Casana, R.

doi:10.1103/physrevd.91.083013

Cited by 3 publications

(2 citation statements)

References 78 publications

(202 reference statements)

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“…A modeling of such trends is presented in Refs. [51,52] (hereafter GC15 and G17, respectively). Making use of the gravitational potential in the Schwarzschild metric we showed that the energy extracted by tides from clumps of plasma orbiting in the accretion disk might produce the rms amplitude of the HF QPOs seen in NS LMXBs.…”

Section: Introductionmentioning

confidence: 99%

Lower-twin-peak quasiperiodic oscillation coherence in x-ray binaries and matter stretched by tides falling onto a compact object

Germanà

2018

Phys. Rev. D

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Low mass x-ray binaries (LMXBs), with either a neutron star (NS) or a black hole, show in their power spectra quasiperiodic oscillations (QPOs). Those at highest frequencies show up in pairs and are named twin peak high frequency QPOs (HF QPOs). Their central frequencies are typical of the orbital motion timescale close to the compact object. HF QPOs are believed to carry unique information on the matter moving in the extreme gravitational field around the compact object. In previous works we highlighted the work done by strong tides on clumps of plasma orbiting in the accretion disk as suitable mechanism to produce the HF QPOs. We showed that the upper of the twin peak HF QPOs seen in NS LMXBs could originate from the tidal circularization of the clump's relativistic orbit, while the lower HF QPO could come from the spiraling clump losing orbital energy. Here we focus on the tidal deformation of a magnetized clump of plasma once tides load energy on it. The likely evolution of the shape of the clump after tidal circularization of the orbit and its subsequent orbital evolution are investigated. In atoll NS LMXBs, a subclass of NS LMXBs less luminous than Z NS LMXBs, the lower HF QPO displays a characteristic behavior of its coherence Q versus its central frequency ν. Q keeps increasing over the range of frequencies ν ∼ 600-850 Hz and then drops abruptly at ν ∼ 900 Hz. We note, for the first time, that such behavior is reproduced by magnetized clumps of plasma stretched by strong tides and falling onto the NS on unstable orbits. The increasing part of Q is drawn by the tidal stretching timescale of the clump all over the orbit. The abrupt drop of Q is dictated by the number of turns the clump makes before reaching the innermost stable bound orbit; afterwards the clump would fall onto the NS. We emphasize the overall behavior of the lower HF QPO coherence as candidate to disclose the innermost stable bound orbit predicted by the general relativity theory in the strong field regime.PACS numbers: 95.30.Sf, 97.80.Jp, 97.10.Gz 1 For a maximally spinning BH the innermost stable bound orbit lies at r = rg, for a Schwarzschild compact object at r = 6 rg. rg = GM/c 2 is the gravitational radius. G gravitational constant, M mass of the compact object and c speed of light. For a 2 M ⊙ neutron star rg ∼ 3 km.

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Section: Introductionmentioning

confidence: 99%

Lower-twin-peak quasiperiodic oscillation coherence in x-ray binaries and matter stretched by tides falling onto a compact object

Germanà

2018

Phys. Rev. D

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“…In a previous work (Ref. [56], hereafter GC15) we have proposed that the amplitude and coherence of the lower HF QPO might originate from the energy released by a clump of plasma spiraling to inner orbits because of the work done by the tidal force, dissipating the orbital energy. In this paper we aim to investigate on the amplitude and coherence of the upper HF QPO [52].…”

Section: Introductionmentioning

confidence: 99%

Upper-twin-peak quasiperiodic oscillation in x-ray binaries and the energy from tidal circularization of relativistic orbits

Germanà

2017

Phys. Rev. D

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High frequency quasiperiodic oscillations (HF QPOs) detected in the power spectra of low mass x-ray binaries (LMXBs) could unveil the fingerprints of gravitation in strong field regime. Using the energy-momentum relation we calculate the energy a clump of plasma orbiting in the accretion disk releases during circularization of its slightly eccentric relativistic orbit. Following previous works, we highlight the strong tidal force as mechanism to dissipate such energy. We show that tides acting on the clump are able to reproduce the observed coherence of the upper HF QPO seen in LMXBs with a neutron star (NS). The quantity of energy released by the clump and relativistic boosting might give a modulation amplitude in agreement with that observed in the upper HF QPO. Both the amplitude and coherence of the upper HF QPO in NS LMXBs could allow us to disclose, for the first time, the tidal circularization of relativistic orbits occurring around a neutron star. PACS numbers: 95.30.Sf, 97.80.Jp, 97.10.Gz

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Lower twin peak quasiperiodic oscillation coherence across luminosity and the tidal stretching time-scale

Germanà

2024

Astrophys Space Sci

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Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasiperiodic oscillations

Cited by 3 publications

References 78 publications

Lower-twin-peak quasiperiodic oscillation coherence in x-ray binaries and matter stretched by tides falling onto a compact object

Lower-twin-peak quasiperiodic oscillation coherence in x-ray binaries and matter stretched by tides falling onto a compact object

Upper-twin-peak quasiperiodic oscillation in x-ray binaries and the energy from tidal circularization of relativistic orbits

Lower twin peak quasiperiodic oscillation coherence across luminosity and the tidal stretching time-scale

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