共查询到20条相似文献，搜索用时 765 毫秒
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J. Crummy A. C. Fabian L. Gallo R. R. Ross 《Monthly notices of the Royal Astronomical Society》2006,365(4):1067-1081
We present a large sample of type 1 active galactic nuclei (AGN) spectra taken with XMM–Newton , and fit them with both the conventional model (a power law and blackbody) and the relativistically blurred photoionized disc reflection model of Ross & Fabian. We find that the disc reflection model is a better fit. The disc reflection model successfully reproduces the continuum shape, including the soft excess, of all the sources. The model also reproduces many features that would conventionally be interpreted as absorption edges. We are able to use the model to infer the properties of the sources, specifically that the majority of black holes in the sample are strongly rotating, and that there is a deficit in sources with an inclination >70°. We conclude that the disc reflection model is an important tool in the study of AGN X-ray spectra. 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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Minfeng Gu Xinwu Cao D. R. Jiang Y. Xu 《Monthly notices of the Royal Astronomical Society》2001,321(2):369-371
The low-frequency radio luminosity is believed to be an indicator of jet power, while the optical/ultraviolet (UV) emission is probably from accretion discs in the nuclei of steep-spectrum radio quasars. We present a correlation between the ratio of radio-to-optical luminosities and the continuum spectral index in blue/UV bands, which might indicate that the continuum shape in blue/UV bands is related to the ratio of jet to accretion power. The results may imply that the spectra and structure of accretion discs are probably affected by the interactions between jets and discs. 相似文献
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We find a significant anticorrelation between the hard X-ray photon index Γ and the Eddington ratio L bol / L Edd for a sample of low-ionization nuclear emission-line regions and local Seyfert galaxies, compiled from literature with Chandra or XMM–Newton observations. This result is in contrast with the positive correlation found in luminous active galactic nuclei (AGN), while it is similar to that of X-ray binaries (XRBs) in the low/hard state. Our result is qualitatively consistent with the spectra produced from advection-dominated accretion flows (ADAFs). It implies that the X-ray emission of low-luminosity active galactic nuclei (LLAGN) may originate from the Comptonization process in ADAF, and the accretion process in LLAGN may be similar to that of XRBs in the low/hard state, which is different from that in luminous AGN. 相似文献
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The physics behind the spectral energy distribution (SED) of blazars remains open.We assembled 36 blazars to tackle the factors that control their SED. Now, many blazar spectra have the "double hump" feature in the radio and far-IR frequencies. For these a parameter,△, is created to characterize the behavior of the SED. We found a significant correlation between the broad-line luminosity (LBLR) and △. Because LBLR is an indicator of the accreting power of the source in blazars, we derived a linear correlation,△∝ (M)1/3. 18, which suggests that the SED of blazars may depend on the accretion rate, like that of BL Lac objects. We also found a significant correlation between (m) and△ for a sample of 11 blazars (out of one of 36)with available black hole masses. This implies the Eddington accretion ratio may influence the shape of the SED of blazars. 相似文献
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S. Vaughan J. Reeves R. Warwick R. Edelson 《Monthly notices of the Royal Astronomical Society》1999,309(1):113-124
We present a systematic analysis of the X-ray spectral properties of a sample of 22 'narrow-line' Seyfert 1 galaxies for which data are available from the ASCA public archive. Many of these sources, which were selected on the basis of their relatively narrow H β linewidth (FWHM ≤2000 km s−1 ), show significant spectral complexity in the X-ray band. Their measured hard power-law continua have photon indices spanning the range 1.6–2.5 with a mean of 2.1, which is only slightly steeper than the norm for 'broad-line' Seyfert 1s. All but four of the sources exhibit a soft excess, which can be modelled as blackbody emission ( T bb ≈100–300 eV) superposed on the underlying power law. This soft component is often so strong that, even in the relatively hard bandpass of ASCA , it contains a significant fraction, if not the bulk, of the X-ray luminosity, apparently ruling out models in which the soft excess is produced entirely through reprocessing of the hard continuum.
Most notably, six of the 22 objects show evidence for a broad absorption feature centred in the energy range 1.1–1.4 keV , which could be the signature of resonance absorption in highly ionized material. A further three sources exhibit 'warm absorption' edges in the 0.7–0.9 keV bandpass. Remarkably, all nine 'absorbed' sources have H β linewidths below 1000 km s−1 , which is less than the median value for the sample taken as a whole. This tendency for very narrow linewidths to correlate with the presence of ionized absorption features in the soft X-ray spectra of NLS1s, if confirmed in larger samples, may provide a further clue in the puzzle of active galactic nuclei. 相似文献
Most notably, six of the 22 objects show evidence for a broad absorption feature centred in the energy range 1.1–1.4 keV , which could be the signature of resonance absorption in highly ionized material. A further three sources exhibit 'warm absorption' edges in the 0.7–0.9 keV bandpass. Remarkably, all nine 'absorbed' sources have H β linewidths below 1000 km s
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Matthew Middleton Chris Done Martin Ward Marek Gierli&#;ski Nick Schurch 《Monthly notices of the Royal Astronomical Society》2009,394(1):250-260
The X-ray quasi-periodic oscillation (QPO) seen in RE J1034+396 is so far unique amongst active galactic nuclei (AGN). Here, we look at another unique feature of RE J1034+396, namely its huge soft X-ray excess, to see if this is related in any way to the detection of the QPO. We show that all potential models considered for the soft energy excess can fit the 0.3–10 keV X-ray spectrum, but the energy dependence of the rapid variability (which is dominated by the QPO) strongly supports a spectral decomposition where the soft excess is from low-temperature Comptonization of the disc emission and remains mostly constant, while the rapid variability is produced by the power-law tail changing in normalization. The presence of the QPO in the tail rather than in the disc is a common feature in black hole binaries (BHBs), but low-temperature Comptonization of the disc spectrum is not generally seen in these systems. The main exception to this is GRS 1915+105, the only BHB which routinely shows super-Eddington luminosities. We speculate that the super-Eddington accretion rates lead to a change in disc structure, and that this also triggers the X-ray QPO. 相似文献
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R. S. Nemmen R. G. Bower A. Babul T. Storchi-Bergmann 《Monthly notices of the Royal Astronomical Society》2007,377(4):1652-1662
The power of jets from black holes is expected to depend on both the spin of the black hole and the structure of the accretion disc in the region of the last stable orbit. We investigate these dependencies using two different physical models for the jet power: the classical Blandford–Znajek (BZ) model and a hybrid model developed by Meier. In the BZ case, the jets are powered by magnetic fields directly threading the spinning black hole while in the hybrid model, the jet energy is extracted from both the accretion disc as well as the black hole via magnetic fields anchored to the accretion flow inside and outside the hole's ergosphere. The hybrid model takes advantage of the strengths of both the Blandford–Payne and BZ mechanisms, while avoiding the more controversial features of the latter. We develop these models more fully to account for general relativistic effects and to focus on advection-dominated accretion flows (ADAFs) for which the jet power is expected to be a significant fraction of the accreted rest mass energy.
We apply the models to elliptical galaxies, in order to see if these models can explain the observed correlation between the Bondi accretion rates and the total jet powers. For typical values of the disc viscosity parameter α∼ 0.04 –0.3 and mass accretion rates consistent with ADAF model expectations, we find that the observed correlation requires j ≳ 0.9 ; that is, it implies that the black holes are rapidly spinning. Our results suggest that the central black holes in the cores of clusters of galaxies must be rapidly rotating in order to drive jets powerful enough to heat the intracluster medium and quench cooling flows. 相似文献
We apply the models to elliptical galaxies, in order to see if these models can explain the observed correlation between the Bondi accretion rates and the total jet powers. For typical values of the disc viscosity parameter α∼ 0.04 –0.3 and mass accretion rates consistent with ADAF model expectations, we find that the observed correlation requires j ≳ 0.9 ; that is, it implies that the black holes are rapidly spinning. Our results suggest that the central black holes in the cores of clusters of galaxies must be rapidly rotating in order to drive jets powerful enough to heat the intracluster medium and quench cooling flows. 相似文献
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Xinwu Cao 《Monthly notices of the Royal Astronomical Society》2002,332(4):999-1004
We consider the power of a relativistic jet accelerated by the magnetic field of an accretion disc. It is found that the power extracted from the disc is mainly determined by the field strength and configuration of the field far from the disc. Comparing it with the power extracted from a rotating black hole, we find that the jet power extracted from a disc can dominate over that from the rotating black hole. However, in some cases, the jet power extracted from a rapidly rotating hole can be more important than that from the disc, even if the poloidal field threading the hole is not significantly larger than that threading the inner edge of the disc. The results imply that the radio-loudness of quasars may be governed by its accretion rate, which might be regulated by the central black hole mass. It is proposed that the different disc field generation mechanisms might be tested against observations of radio-loud quasars if their black hole masses are available. 相似文献
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Xue-Guang Zhang D. Dultzin-Hacyan Ting-Gui Wang 《Monthly notices of the Royal Astronomical Society》2007,376(3):1335-1340
In this paper, the sizes of the broad emission line regions (BLRs) and black hole (BH) masses of double-peaked broad low-ionization emission line emitters (DBP emitters) are compared using different methods: virial BH masses versus BH masses from stellar velocity dispersions, the size of BLRs from the continuum luminosity versus the size of BLRs from the accretion disc model. First, the virial BH masses of DBP emitters estimated by the continuum luminosity and linewidth of broad Hβ are about six times (a much larger value, if including another DBP emitters, of which the stellar velocity dispersions are traced by the linewidths of narrow emission lines) larger than the BH masses estimated from the relation M BH –σ which is a more accurate relation to estimate BH masses. Second, the sizes of the BLRs of DBP emitters estimated by the empirical relation of R BLR – L 5100 Å are about three times (a much larger value, if including another DBP emitters, of which the stellar velocity dispersions are traced by the linewidths of narrow emission lines) larger than the mean flux-weighted sizes of BLRs of DBP emitters estimated by the accretion disc model. The higher electron density of BLRs of DBP emitters would be the main reason which leads to smaller size of BLRs than the predicted value from the continuum luminosity. 相似文献
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Rebecca G. Martin 《Monthly notices of the Royal Astronomical Society》2008,387(2):830-838
We consider the properties of the warped accretion disc in NGC 4258 which is delineated by maser emission. We use our analytical models to consider whether the disc could be warped by Lense–Thirring precession. We show that such models fit the shape of the disc well and we determine the goodness of fit for various combinations of the warp radius and the disc and black hole configurations. Though the fits are compelling evidence, we note that such a model has implications for the formation and longevity of the disc which might be problematic for the current understanding of Seyfert galaxies. 相似文献
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P.T. O'Brien K. Page J.N. Reeves K. Pounds M.J.L. Turner E.M. Puchnarewicz 《Monthly notices of the Royal Astronomical Society》2001,327(4):L37-L41
We present XMM-Newton observations of Mrk 359, the first narrow-line Seyfert 1 galaxy (NLS1) discovered. Even among NLS1s, Mrk 359 is an extreme case with extraordinarily narrow optical emission lines. The XMM-Newton data show that Mrk 359 has a significant soft X-ray excess which displays only weak absorption and emission features. The continuum, including reflection, is flatter than that of the typical NLS1, with . A strong emission line of equivalent width ≈200 eV is also observed, centred near 6.4 keV. We fit this emission with two line components of approximately equal strength: a broad iron line from an accretion disc and a narrow, unresolved core. The unresolved line core has an equivalent width of ≈120 eV and is consistent with fluorescence from neutral iron in distant reprocessing gas, possibly in the form of a 'molecular torus'. Comparison of the narrow-line strengths in Mrk 359 and other low–moderate luminosity Seyfert 1 galaxies with those in QSOs suggests that the solid angle subtended by the distant reprocessing gas decreases with increasing active galactic nucleus luminosity. 相似文献
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G. Matt 《Astronomische Nachrichten》2008,329(2):151-154
In this paper I will review, in an unavoidably incomplete and biased way, the main results obtained by XMM‐Newton on Active Galactic Nuclei. I will then highlight the major issues still open in which XMM‐Newton can still give important contributions, expecially if the observing programs will shift in the future towards more long exposures of single objects and observations of large samples. I will also argue in favour of a legacy program consisting of good S/N observations of a flux‐limited, sizeable sample of AGN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Piotr T. &#;ycki Agata Ró&#;a&#;ska 《Monthly notices of the Royal Astronomical Society》2001,325(1):197-207
A number of recent results from X-ray observations of active galactic nuclei involving the Fe K α line (reduction of line variability compared with the X-ray continuum variability, the X-ray 'Baldwin effect') were attributed to the presence of a hot, ionized skin of an accretion disc, suppressing emission of the line. The ionized skin appears as a result of the thermal instability of X-ray irradiated plasma. We test this hypothesis by computing the Thomson thickness of the hot skin on top of the αP tot Shakura–Sunyaev disc, by simultaneously solving the vertical structure of both the hot skin and the disc. We then compute a number of relations between observable quantities, e.g. the hard X-ray flux, amplitude of the observed reprocessed component, relativistic smearing of the K α line and rms variability of the hard X-rays. These relations can be compared with present and future observations. We point out that this mechanism is unlikely to explain the behaviour of the X-ray source in MCG–6-30-15, where there are a number of arguments against the existence of a thick hot skin, but it can work for some other Seyfert 1 galaxies. 相似文献
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L. C. Gallo 《Astronomische Nachrichten》2006,327(10):1076-1078
In recent work it was demonstrated that narrow‐line Seyfert 1 galaxies, which possessed spectral complexity in the 2–10 keV band were at the same time X‐ray weak. In this contribution I show how X‐ray weakness can be understood in the context of reflection and light bending picture. In fact, X‐ray weakness should be expected from objects that are in a reflection dominated state. With simultaneous UV and X‐ray data available with most XMM‐Newton observations, an estimate of the X‐ray weakness is relatively straightforward. As such, it is an easy way to substantiate conclusions of reflection dominated spectra, and we use this method to examine recent claims. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献