共查询到20条相似文献，搜索用时 501 毫秒
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Fang Yang Chen Hu Yan-Mei Chen Jian-Min Wang 《中国天文和天体物理学报》2007,7(3):353-363
We compiled a sample of 98 radio-quiet active galactic nuclei observed by ASCA, Chandra, XMM-Newton, INTEGRAL and Swift with the aim of testing the formation of hot corona and the magnetic shear stress operating in a disk-corona system. We found a strong correlation between the hard X-ray luminosity, bolometric luminosity L Bol and Eddington luminosity LEdd, in the sense that the fraction f of hard X-ray to the bolometric luminosity is inversely proportional to the Eddington ratio. This correlation favors the shear stress tensor being of the form of trφ∝ Pgas, with which the disk-corona structure is stable. 相似文献
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Marek Gierli&#;ski Chris Done Kim Page 《Monthly notices of the Royal Astronomical Society》2009,392(3):1106-1114
We build a simple model of the optical/ultraviolet (UV) emission from irradiation of the outer disc by the inner disc and coronal emission in black hole binaries. We apply this to the broad-band Swift data from the outburst of the black hole binary XTE J1817−330 to confirm previous results that the optical/UV emission in the soft state is consistent with a reprocessing a constant fraction of the bolometric X-ray luminosity. However, this is very surprising as the disc temperature drops by more than a factor of 3 in the soft state, which should produce a marked change in the reprocessing efficiency. The easiest way to match the observed constant reprocessed fraction is for the disc skin to be highly ionized (as suggested 30 yr ago by van Paradijs), so that the bulk of the disc flux is reflected and only the hardest X-rays heat the disc. The constant reprocessed fraction also favours direct illumination of the disc over a scattering origin as the optical depth/solid angle of any scattering material (wind/corona) over the disc should decrease as the source luminosity declines. By contrast, the reprocessed fraction increases very significantly (by a factor of ∼6) as the source enters the hard state. This dramatic change is not evident from X-ray/UV flux correlations as it is masked by bandpass effects. However, it does not necessarily signal a change in emission, for example, the emergence of the jet dominating the optical/UV flux as the reflection albedo must change with the dramatic change in spectral shape. 相似文献
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Zhan-Kui Lü 《中国天文和天体物理学报》2009,9(7)
Like the investigation of double white dwarf (DWD) systems, strange dwarf (SD) - white dwarf (WD) system evolution in Laser Interferometer Space Antenna (LISA)'s absolute amplitude-frequency diagram is investigated. Since there is a strange quark core inside an SD, SDs' radii are significantly smaller than the value predicted by the standard WD model, which may strongly affect the gravitational wave (GW) signal in the mass-transferring phases of binary systems. We study how an SD-WD binary evolves across LISA's absolute amplitude-frequency diagram. In principle, we provide an executable way to detect SDs in the Galaxy's DWD systems by radically new windows offered by GW detectors. 相似文献
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The fluctuating-accretion model of Lyubarskii and its extension by Kotov, Churazov & Gilfanov seek to explain the spectral-timing properties of the X-ray variability of accreting black holes in terms of inward-propagating mass accretion fluctuations produced at a broad range of radii. The fluctuations modulate the X-ray emitting region as they move inwards and can produce temporal-frequency-dependent lags between energy bands, and energy-dependent power spectral densities (PSDs) as a result of the different emissivity profiles, which may be expected at different X-ray energies. Here, we use a simple numerical implementation to investigate in detail the X-ray spectral-timing properties of the model and their relation to several physically interesting parameters, namely the emissivity profile in different energy bands, the geometrical thickness and viscosity parameter of the accretion flow, the strength of damping on the fluctuations and the temporal coherence (measured by the 'quality factor', Q ) of the fluctuations introduced at each radius. We find that a geometrically thick flow with large viscosity parameter is favoured, and we confirm that the predicted lags are quite robust to changes in the emissivity profile and physical parameters of the accretion flow, which may help to explain the similarity of the lag spectra in the low/hard and high/soft states of Cyg X-1. We also demonstrate the model regime where the light curves in different energy bands are highly spectrally coherent. We compare model predictions directly to X-ray data from the narrow line Seyfert 1 galaxy NGC 4051 and the black hole X-ray binary (BHXRB) Cyg X-1 in its high/soft state, and we show that this general scheme can reproduce simultaneously the time lags and energy-dependence of the PSD. 相似文献
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Jeanette Gladstone Chris Done Marek Gierli&#;ski 《Monthly notices of the Royal Astronomical Society》2007,378(1):13-22
We systematically analyse all the available X-ray spectra of disc accreting neutron stars (atolls and millisecond pulsars) from the RXTE data base. We show that while all these have similar spectral evolution as a function of mass accretion rate, there are also subtle differences. There are two different types of hard/soft transition, those where the spectrum softens at all energies, leading to a diagonal track on a colour–colour diagram, and those where only the higher energy spectrum softens, giving a vertical track. The luminosity at which the transition occurs is correlated with this spectral behaviour, with the vertical transition at L / L Edd ∼ 0.02 while the diagonal one is at ∼0.1. Superimposed on this is the well-known hysteresis effect, but we show that classic, large-scale hysteresis occurs only in the outbursting sources, indicating that its origin is in the dramatic rate of change of mass accretion rate during the disc instability. We show that the long-term mass accretion rate correlates with the transition behaviour, and speculate that this is due to the magnetic field being able to emerge from the neutron star surface for low average mass accretion rates. While this is not strong enough to collimate the flow except in the millisecond pulsars, its presence may affect the inner accretion flow by changing the properties of the jet. 相似文献
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J. Larwood 《Monthly notices of the Royal Astronomical Society》1998,299(2):L32-L36
In this Letter, recent results on the nodal precession of accretion discs in close binaries are applied to the discs in some X-ray binary systems. The ratio between the tidally forced precession period and the binary orbital period is given, as well as the condition required for the rigid precession of gaseous Keplerian discs. Hence the minimum precessional period that may be supported by a fluid Keplerian disc is determined. It is concluded that near-rigid body precession of tilted accretion discs can occur and generally reproduce observationally inferred precession periods, for reasonable system parameters. In particular, long periods in SS 433, Her X-1, LMC X-4 and SMC X-1 can be fitted by the tidal model. It is also found that the precession period that has been tentatively put forward for Cyg X-2 cannot be accommodated by a tidally precessing disc model for any realistic choice of system parameters. 相似文献
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Disc-accreting neutron stars come in two distinct varieties, atolls and Z sources, named after their differently shaped tracks on a colour–colour diagram as the source luminosity changes. Here we present analysis of three transient atoll sources showing that there is an additional branch in the colour–colour diagram of atoll sources which appears at very low luminosities. This new branch connects to the top of previously known C-shaped (atoll) path, forming a horizontal track where the average source flux decrease from right to left. This turns the C-shape into a Z. Thus both atolls and Z sources share the same topology on the colour–colour diagram and evolve in similar way, as a function of increasing averaged mass accretion rate. This strongly favours models in which the underlying geometry of these sources changes in similar ways. A possible scenario is one where the truncated disc approaches the neutron star when the accretion rate increases, but in the atolls the disc is truncated by evaporation (similarly to black holes), and in the Z sources it is truncated by the magnetic field. 相似文献
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Rebecca G. Martin Christopher A. Tout J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2008,387(1):188-196
The microquasar GRO J1655−40 has a black hole with spin angular momentum apparently misaligned to the orbital plane of its companion star. We analytically model the system with a steady-state disc warped by Lense–Thirring precession and find the time-scale for the alignment of the black hole with the binary orbit. We make detailed stellar evolution models so as to estimate the accretion rate and the lifetime of the system in this state. The secondary can be evolving at the end of the main sequence or across the Hertzsprung gap. The mass-transfer rate is typically 50 times higher in the latter case but we find that, in both the cases, the lifetime of the mass-transfer state is at most a few times the alignment time-scale. The fact that the black hole has not yet aligned with the orbital plane is therefore consistent with either model. We conclude that the system may or may not have been counter aligned after its supernova kick but that it is most likely to be close to alignment rather than counter alignment now. 相似文献
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Pasi Hakala Linnea Hjalmarsdotter Diana C. Hannikainen Panu Muhli † 《Monthly notices of the Royal Astronomical Society》2009,394(2):892-899
Since its discovery in 1990, UW CrB (also known as MS1603+2600) has remained a peculiar source without firm classification. Our current understanding is that it is an accretion disc corona (ADC) low-mass X-ray binary. In this paper, we present results from our photometric campaign dedicated to studying the changing morphology of the optical light curves. We find that the optical light curves show remarkable evidence for strongly evolving light curve shapes. In addition, we find that these changes show a modulation at a period of ∼5 d. We interpret these changes as either due to strong periodic accretion disc warping or due to other geometrical changes because of disc precession at a period of 5 d. Finally, we have detected 11 new optical bursts, the phase distribution of which supports the idea of a vertically extended asymmetric accretion disc. 相似文献
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Evolution of black hole intermediate-mass X-ray binaries: the influence of a circumbinary disc 总被引：1，自引：0，他引：1
We report the results of a systematic timing analysis of RXTE observations of GRS 1915+105 when the source was in its variability class θ, characterized by alternating soft and hard states on a time-scale of a few hundred seconds. The aim was to examine the high-frequency part of the power spectrum in order to confirm the hectohertz quasi-periodic oscillations (QPO) previously reported from observations from mixed variability behaviours. During the hard intervals (corresponding to state C in the classification of Belloni et al.), we find a significant QPO at a frequency of ∼170 Hz, although much broader (Q∼2) than previously reported. No other significant peak is observed at frequencies >30 Hz. A time-resolved spectral analysis of selected observations shows that the hard intervals from class θ show a stronger and steeper (Γ= 2.8–3.0) power-law component than hard intervals from other classes. We discuss these results in the framework of hectohertz QPOs reported from GRS 1915+105 and other black hole binaries. 相似文献
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Black hole accretion discs: reality confronts theory 总被引：2，自引：0，他引：2
Marek Gierli&#;ski Chris Done 《Monthly notices of the Royal Astronomical Society》2004,347(3):885-894
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Marek Gierli&#;ski Chris Done Kim Page 《Monthly notices of the Royal Astronomical Society》2008,388(2):753-760
The key aspect of the very successful truncated disc model for the low/hard X-ray spectral state in black hole binaries is that the geometrically thin disc recedes from the last stable orbit at the transition to this state. This has recently been challenged by direct observations of the low/hard state disc from CCD data. We reanalyse the Swift and RXTE campaign covering the 2006 outburst of XTE J1817−330, and show that these data actually strongly support the truncated disc model as the transition spectra unambiguously show that the disc begins to recede as the source leaves the disc-dominated soft state. The disc radius inferred for the proper low/hard state is less clear-cut, but we show that the effect of irradiation from the energetically dominant hot plasma leads to an underestimate of the disc radius by a factor of 2–3 in this state. This may also produce the soft excess reported in some hard-state spectra. The inferred radius becomes still larger when the potential difference in stress at the inner boundary, increased colour temperature correction from incomplete thermalization of the irradiation, and loss of observable disc photons from Comptonization in the hot plasma is taken into account. We conclude that the inner disc radius in XTE J1817−330 in the low/hard spectral state is at least six to eight times that seen in the disc-dominated high/soft state, and that recession of the inner disc is the trigger for the soft-hard-state transition, as predicted by the truncated disc models. 相似文献