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- Feroci, M., et al.
(författare)
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The Large Observatory for X-ray Timing (LOFT)
- 2012
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 34:2, s. 415-444
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Tidskriftsartikel (refereegranskat)abstract
- High-time-resolution X-ray observations of compact objects provide direct access to strong-field gravity, to the equation of state of ultradense matter and to black hole masses and spins. A 10 m(2)-class instrument in combination with good spectral resolution is required to exploit the relevant diagnostics and answer two of the fundamental questions of the European Space Agency (ESA) Cosmic Vision Theme "Matter under extreme conditions", namely: does matter orbiting close to the event horizon follow the predictions of general relativity? What is the equation of state of matter in neutron stars? The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionise the study of collapsed objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. Thanks to an innovative design and the development of large-area monolithic silicon drift detectors, the Large Area Detector (LAD) on board LOFT will achieve an effective area of similar to 12 m(2) (more than an order of magnitude larger than any spaceborne predecessor) in the 2-30 keV range (up to 50 keV in expanded mode), yet still fits a conventional platform and small/medium-class launcher. With this large area and a spectral resolution of < 260 eV, LOFT will yield unprecedented information on strongly curved spacetimes and matter under extreme conditions of pressure and magnetic field strength.
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| 2. |
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| 3. |
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| 4. |
- Abramowicz, Marek A, 1945, et al.
(författare)
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A note on the slope-shift anticorrelation in the neutron star kHz QPOs data
- 2005
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Ingår i: n Proceedings of RAGtime 6/7: Workshops on black holes and neutron stars. - 807248334X
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Konferensbidrag (refereegranskat)abstract
- Observations show that the upper νU and lower νL of the ``twin peak'' high frequency QPOs in neutron star sources vary along lines νU = AνL + B in a frequency-frequency plot, and that their ratios νU/νL cluster near the value 3/2. This behaviour is well consistent with the predictions of the non-linear resonance model for QPOs. In this Note, we further explore our recent finding that the coefficients A, B of the frequency-frequency lines for individual sources are anticorrelated. In the (A,B) plane, they occupy rather a narrow region along the line A = 3/2 - B/600 Hz. We show that this observational property of QPOs also follows from the resonance model
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| 5. |
- Abramowicz, Marek A, 1945, et al.
(författare)
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Epicyclic frequencies derived from the effective potential: simple and practical formulae
- 2005
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Ingår i: Astrophys. Space Sci.. - : Springer Science and Business Media LLC. - 0004-640X. ; 300:1-3, s. 127-136
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Tidskriftsartikel (refereegranskat)abstract
- We present and discuss a short and simple derivation of orbital epicyclic frequencies for circular geodesic orbits in stationary and axially symmetric spacetimes. Such spacetimes include as special cases analytically known black hole Kerr and Schwarzschild spacetimes, as well as the analytic Hartle-Thorne spacetime and all numerically constructed spacetimes relevant for rotating neutron stars. Our derivation follows directly from energy and angular momentum conservation and it uses the concept of the effective potential. It has never been published, except for a few special cases, but it has already become a part of the common knowledge in the field.
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| 6. |
- Abramowicz, Marek A, 1945, et al.
(författare)
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Mass of a Black Hole Firewall
- 2014
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Ingår i: Physical Review Letters. - 0031-9007. ; 112:9
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Tidskriftsartikel (refereegranskat)abstract
- Quantum entanglement of Hawking radiation has been supposed to give rise to a Planck density "firewall" near the event horizon of old black holes. We show that Planck density firewalls are excluded by Einstein's equations for black holes of mass exceeding the Planck mass. We find an upper limit of 1/(8 pi M) to the surface density of a firewall in a Schwarzschild black hole of mass M, translating for astrophysical black holes into a firewall density smaller than the Planck density by more than 30 orders of magnitude. A strict upper limit on the firewall density is given by the Planck density times the ratio M-Pl/(8 pi M).
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| 7. |
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| 8. |
- 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. 8-17
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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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| 9. |
- Abramwicz, M A, et al.
(författare)
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Possible Suppression of Magnetorotational Instability by Rapid Radial Flow
- 2013
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Ingår i: Acta Astronomica. - 0001-5237. ; 63:2, s. 267-273
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Tidskriftsartikel (refereegranskat)abstract
- By investigating the magnetorotational instability (MRI) in a region of rapidly varying accretion-disk thickness, e.g., in the ISCO region, we find a limit to the applicability of a recent finding by Balbus (2012) that the MRI is present also in the region of Rayleigh-unstable flow. RAMOWICZ MA, 1988, ASTROPHYSICAL JOURNAL, V332, P646
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| 10. |
- 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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