| 1. |
- Abramowicz, Marek A, 1945-, et al.
(författare)
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And yet it's expanding
- 2007
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Ingår i: Acta Astronomica. - 0001-5237. ; 57:2, s. 139-148
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Tidskriftsartikel (refereegranskat)
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| 2. |
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| 3. |
- Abramowicz, Marek A, 1945-, et al.
(författare)
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The Twin Peak QPOs in Neutron Star and Black Hole Sources: What is explained, and What is not
- 2007
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Ingår i: Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias). ; 27, s. 8
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Konferensbidrag (refereegranskat)abstract
- The resonance model proposed in 2000 by Kluzniak and Abra-mo-wicz, explains the twin peak, high frequency, quasi periodic oscillations (HF QPOs) observed in the X-ray flux from black hole and neutron stars, as a non-linear resonance in modes of oscillations of accretion flows in strong gravity. While several important physical questions remain unanswered, recent observations of HF QPOs provide direct evidence of non-linear resonances. This article gives an up to date (May 2006) review of what has been explained, and what has not been explained, by the resonance model.
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| 4. |
- Abramowicz, Marek A, 1945-, et al.
(författare)
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Twin paradox on the photon sphere
- 2007
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Ingår i: PHYSICAL REVIEW A. - 1050-2947. ; 75:4
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Blaes, Omer, et al.
(författare)
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Epicyclic Oscillations of Fluid Bodies: Newtonian Nonslender Torus
- 2007
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Ingår i: Astrophysical Journal. - 0004-637X. ; 665:1, s. 642-653
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Tidskriftsartikel (refereegranskat)abstract
- We study epicyclic oscillations of fluid tori around black holes (in the Paczyński-Wiita potential) and derive exact analytic expressions for their radial and vertical eigenfrequencies νr and νz to second-order accuracy in the width of the torus. We prove that pressure effects make the eigenfrequencies smaller than those for free particles. However, the particular ratio νz/νr=3/2, which is important for the theory of high-frequency quasi-periodic oscillations (QPOs), occurs when the fluid tori epicyclic frequencies νr and νz are about 15% higher than the ones corresponding to free particles. Our results therefore suggest that previous estimates of black hole spins from QPOs have produced values that are too high.
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| 6. |
- Bursa, M., et al.
(författare)
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The timescale of encircling light
- 2007
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Ingår i: Silesian University in Opava. ; s. 21-25
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Konferensbidrag (refereegranskat)abstract
- We show that in some astronomical sources containing black holes, the signature of the circular photon orbit may be detected by searching for the shortest timescale in the variability data. A positive detection would provide the direct empirical support for Einstein's general relativity in its super-strong field limit, relevant to black holes.
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| 7. |
- Kluzniak, Wlodek, et al.
(författare)
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Nonlinear resonance in the accretion disk of a millisecond pulsar
- 2007
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Ingår i: Astrophysics Journal. - 0067-0049. ; 603:2, s. 89-92
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Tidskriftsartikel (refereegranskat)abstract
- Two simultaneous frequencies of quasi-periodic millisecond modulation of the X-ray flux (twin kilohertz quasi-periodic oscillations) have recently been detected in an accreting 2.5 ms X-ray pulsar. Their difference, equal to about ½ of the neutron star spin rate, clearly indicates that resonant oscillations of the accretion disk have been observed. Similar nonlinear resonances may be spontaneously excited in the accretion disk in the absence of a pulsar, e.g., in black holes. We identify modes of disk oscillations whose frequencies are in agreement with the two observed ones when the rotating neutron star is modeled with realistic equations of state.
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| 8. |
- Kluzniak, W., et al.
(författare)
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QPOs and Resonance in Accretion Disks
- 2007
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Ingår i: Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias). ; 27, s. 18-25
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Konferensbidrag (refereegranskat)abstract
- We review arguments suggesting that millisecond variability detected in the X-ray flux of LMXBs has its origin in oscillation modes of the accretion disk. The twin high-frequency QPOs observed in microquasars seem to be related to the twin kHz QPOs in neutron-star systems, and both phenomena are likely the result of a non-linear resonance in the accretion disk that is possible only in strong-field gravity. A presumed 3:2 eigenfrequency ratio of the resonant modes corresponds to the 3:2 QPO frequency ratio clearly detected in black-hole systems, as well as to the more complex distribution of kHz QPO frequency pairs in neutron stars.
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| 9. |
- Srámková, Eva, et al.
(författare)
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Oscillations of tori in the pseudo-Newtonian potential
- 2007
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Ingår i: Astronomy and astrophysics. - 00046361. ; 467:2, s. 641-646
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Tidskriftsartikel (refereegranskat)abstract
- Context: The high-frequency quasi-periodic oscillations (HF QPOs) in neutron star and stellar-mass black hole X-ray binaries may be the result of a resonance between the radial and vertical epicyclic oscillations in strong gravity. Aims: In this paper we investigate the resonant coupling between the epicyclic modes in a torus in a strong gravitational field. Methods: We perform numerical simulations of axisymmetric constant angular momentum tori in the pseudo-Newtonian potential. The epicyclic motion is excited by adding a constant radial velocity to the torus. Results: We verify that slender tori perform epicyclic motions at the frequencies of free particles, but the epicyclic frequencies decrease as the tori grow thicker. More importantly, and in contrast to previous numerical studies, we do not find a coupling between the radial and vertical epicyclic motions. The appearance of other modes than the radial epicyclic motion in our simulations is rather due to small numerical deviations from exact equilibrium in the initial state of our torus. Conclusions: We find that there is no pressure coupling between the two axisymmetric epicyclic modes as long as the torus is symmetric with respect to the equatorial plane. However we also find that there are other modes in the disc that may be more attractive for explaining the HF QPOs.
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