| 1. |
- Feroci, M., et al.
(författare)
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The large observatory for x-ray timing
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819496126
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Konferensbidrag (refereegranskat)abstract
- The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
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| 2. |
- Feroci, M., et al.
(författare)
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LOFT - The large observatory for x-ray timing
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9780819491442 ; , s. 84432D-
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Konferensbidrag (refereegranskat)abstract
- The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of <5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO's to yearlong transient outbursts. In this paper we report the current status of the project.
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| 3. |
- 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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| 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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The correlations and anticorrelations in QPO data
- 2005
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Ingår i: Astronomische Nachrichten. - : Wiley. - 0004-6337 .- 1521-3994. ; 326:9, s. 864-866
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Tidskriftsartikel (refereegranskat)abstract
- Double peak kHz QPO frequencies in neutron star sources varies in time by a factor of hundreds Hz while in microquasar sources the frequencies are fixed and located at the line ν2 - ν1 in the frequency-frequency plot. The crucial question in the theory of twin HFQPOs is whether or not those observed in neutron-star systems are essentially different from those observed in black holes. In black hole systems the twin HFQPOs are known to be in a 3:2 ratio for each source. At first sight, this seems not to be the case for neutron stars. For each individual neutron star, the upper and lower kHz QPO frequencies, ν2 and ν1, are linearly correlated, ν2 = ν1 + B, with the slope A < 1.5, i.e., the frequencies definitely are not in a 1.5 ratio. In this contribution we show that when considered jointly on a frequency-frequency plot, the data for the twin kHz QPO frequencies in several (as opposed to one) neutron stars uniquely pick out a certain preferred frequency ratio that is equal to 1.5 for the six sources examined so far.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- Bursa, M., et al.
(författare)
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The upper kilohertz quasi-periodic oscillation: a gravitationally lensed vertical oscillation
- 2005
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Ingår i: Astrophysical Journal, Letters. - 0067-0049. ; 617:1
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Tidskriftsartikel (refereegranskat)abstract
- We show that a luminous torus orbiting a Schwarzschild black hole gives rise to a periodically varying flux of radiation when oscillating along its own axis, even though the source of radiation is steady and perfectly axisymmetric. This implies that the simplest oscillation mode in an accretion flow, axisymmetric up and down motion at the meridional epicyclic frequency, may be directly observable when it occurs in the inner parts of accretion flow around neutron stars and black holes. The high-frequency modulations of the X-ray flux observed in low-mass X-ray binaries at two frequencies (twin kilohertz quasi-periodic oscillations) could then be a signature of strong gravity both because radial and meridional oscillations have different frequencies in non-Newtonian gravity and because strong gravitational deflection of light rays causes the flux of radiation to be modulated at the higher frequency.
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| 9. |
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| 10. |
- 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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