首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
We model the optical to X-ray continuum spectrum of the narrow-line Seyfert 1 galaxy RE J1034+396. We show that the flat optical spectrum is consistent with emission from an irradiated accretion disc. The X-ray emission can be modelled with a disc blackbody and a Comptonized component. The temperature at the inner edge of the disc     Using this constraint, we show that the flat optical spectrum is consistent with emission from the irradiatively heated outer part of the accretion disc. We constrain the outer radius of the optically thick disc     and the inner radius of the irradiation-dominated region     . Our optical and X-ray spectral fits indicate a mass     , and do not rule out a low (i.e. face-on) inclination angle for the system.  相似文献   

2.
The central engines of active galactic nuclei (AGN) contain cold, dense material as well as hot X-ray-emitting gas. The standard paradigm for the engine geometry is a cold thin disc sandwiched between hot X-ray coronae. Strong support for this geometry in Seyferts comes from the study of fluorescent iron line profiles, although the evidence is not ubiquitously airtight. The thin disc model of line profiles in AGN and in X-ray binaries should still be benchmarked against other plausible possibilities. One proposed alternative is an engine consisting of dense clouds embedded in an optically thin, geometrically thick X-ray-emitting engine. This model is also motivated by studies of geometrically thick engines such as advection-dominated accretion flows (ADAFs). Here we compute the reprocessed iron line profiles from dense clouds embedded in geometrically thick, optically thin X-ray-emitting discs near a Schwarzschild black hole. We consider a range of cloud distributions and disc solutions, including ADAFs, pure radial infall and bipolar outflows. We find that such models can reproduce line profiles similar to those from geometrically thin, optically thick discs and might help alleviate some of the problems encountered from the latter. Thus, independent of thin discs, thick disc engines can also exhibit iron line profiles if embedded dense clouds can survive long enough to reprocess radiation.  相似文献   

3.
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   

4.
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   

5.
Over the last few years X-ray observations of broad-line radio galaxies (BLRGs) by ASCA , RXTE and BeppoSAX have shown that these objects seem to exhibit weaker X-ray reflection features (such as the iron K α line) than radio-quiet Seyferts. This has lead to speculation that the optically thick accretion disc in radio-loud active galactic nuclei (AGN) may be truncated to an optically thin flow in the inner regions of the source. Here, we propose that the weak reflection features are a result of reprocessing in an ionized accretion disc. This would alleviate the need for a change in accretion geometry in these sources. Calculations of reflection spectra from an ionized disc for situations expected in radio-loud AGN (high accretion rate, moderate-to-high black hole mass) predict weak reprocessing features. This idea was tested by fitting the ASCA spectrum of the bright BLRG 3C 120 with the constant density ionized disc models of Ross & Fabian. A good fit was found with an ionization parameter of   ξ ∼4000 erg cm s-1  and the reflection fraction fixed at unity. If observations of BLRGs by XMM-Newton show evidence for ionized reflection then this would support the idea that a high accretion rate is likely required to launch powerful radio jets.  相似文献   

6.
We solve for the structure of a hot accretion disc with unsaturated thermal Comptonization of soft photons and with advection, generalizing the classical model of Shapiro et al. The upper limit on the accretion rate due to advection constrains the luminosity to ≲ 0.15 y3/5 α7/5 of the Eddington limit, where y and α are the Compton and viscosity parameters, respectively. The characteristic electron temperature and Thomson optical depth of the inner flow at accretion rates within an order of magnitude of that upper limit are ∼ 109 K and ∼ 1, respectively. The resulting spectra are then in close agreement with the X-ray and soft γ-ray spectra from black hole binaries in the hard state and Seyferts. At low accretion rates, bremsstrahlung becomes the dominant radiative process.  相似文献   

7.
We investigate the polarization properties of Comptonized X-rays from relativistic jets in active galactic nuclei (AGN) using Monte Carlo simulations. We consider three scenarios commonly proposed for the observed X-ray emission in AGN: Compton scattering of blackbody photons emitted from an accretion disc; scattering of cosmic microwave background (CMB) photons and self-Comptonization of intrinsically polarized synchrotron photons emitted by jet electrons. Our simulations show that for Comptonization of disc and CMB photons, the degree of polarization of the scattered photons increases with the viewing inclination angle with respect to the jet axis. In both cases, the maximum linear polarization is  ≈20 per cent  . In the case of synchrotron self-Comptonization (SSC), we find that the resulting X-ray polarization depends strongly on the seed synchrotron photon injection site, with typical fractional polarizations   P ≈ 10–20 per cent  when synchrotron emission is localized near the jet base, while   P ≈ 20–70 per cent  for the case of uniform emission throughout the jet. These results indicate that X-ray polarimetry may be capable of providing unique clues to identify the location of particle acceleration sites in relativistic jets. In particular, if synchrotron photons are emitted quasi-uniformly throughout a jet, then the observed degree of X-ray polarization may be sufficiently different for each of the competing X-ray emission mechanisms (synchrotron, SSC or external Comptonization) to determine which is the dominant process. However, X-ray polarimetry alone is unlikely to be able to distinguish between disc and CMB Comptonization.  相似文献   

8.
We present a general relativistic accretion disc model and its application to the soft-state X-ray spectra of black hole binaries. The model assumes a flat, optically thick disc around a rotating Kerr black hole. The disc locally radiates away the dissipated energy as a blackbody. Special and general relativistic effects influencing photons emitted by the disc are taken into account. The emerging spectrum, as seen by a distant observer, is parametrized by the black hole mass and spin, the accretion rate, the disc inclination angle and the inner disc radius.
We fit the ASCA soft-state X-ray spectra of LMC X-1 and GRO J1655-40 by this model. We find that, having additional limits on the black hole mass and inclination angle from optical/UV observations, we can constrain the black hole spin from X-ray data. In LMC X-1 the constraint is weak, and we can only rule out the maximally rotating black hole. In GRO J1655-40 we can limit the spin much better, and we find 0.68 a 0.88 . Accretion discs in both sources are radiation-pressure dominated. We do not find Compton reflection features in the spectra of any of these objects.  相似文献   

9.
  相似文献   

10.
We present Fe Kα line profiles from and images of relativistic discs with finite thickness around a rotating black hole using a novel code. The line is thought to be produced by iron fluorescence of a relatively cold X-ray-illuminated material in the innermost parts of the accretion disc and provides an excellent diagnostic of accretion flows in the vicinity of black holes. Previous studies have concentrated on the case of a thin, Keplerian accretion disc. This disc must become thicker and sub-Keplerian with increasing accretion rates. These can affect the line profiles and in turn can influence the estimation of the accretion disc and black hole parameters from the observed line profiles. We here embark on, for the first time, a fully relativistic computation which offers key insights into the effects of geometrical thickness and the sub-Keplerian orbital velocity on the line profiles. We include all relativistic effects such as frame-dragging, Doppler boost, time dilation, gravitational redshift and light bending. We find that the separation and the relative height between the blue and red peaks of the line profile diminish as the thickness of the disc increases. This code is also well suited to produce accretion disc images. We calculate the redshift and flux images of the accretion disc and find that the observed image of the disc strongly depends on the inclination angle. The self-shadowing effect appears remarkable for a high inclination angle, and leads to the black hole shadow being in this case, completely hidden by the disc itself.  相似文献   

11.
Observations suggest that accretion discs in many X-ray binaries are likely flared. An outer edge of the disc intercepts radiation from the central X-ray source. Part of that radiation is absorbed and re-emitted in the optical/UV spectral ranges. However, a large fraction of that radiation is reflected and appears in the broad-band X-ray spectrum as a Compton reflection bump. This radiation is delayed and variability is somewhat smeared compared with the intrinsic X-ray radiation. We compute response functions for flat and flared accretion discs and for isotropic and anisotropic X-ray sources. A simple approximation for the response function which is valid in the broad range of the disc shapes and inclinations, inner and outer radii, and the plasma bulk velocity is proposed. We also study the impact of the X-ray reprocessing on temporal characteristics of X-ray binaries such as the power spectral density, auto- and cross-correlation functions, and time/phase lags. We propose a reprocessing model which explains the secondary peaks in the phase lag Fourier spectra observed in Cyg X-1 and other Galactic black hole sources. The position of the peaks could be used to determine the size of the accretion disc.  相似文献   

12.
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   

13.
Fluorescent iron line profiles currently provide the best diagnostic for engine geometries of active galactic nuclei (AGN). Here we construct a method for calculating the relativistic iron line profile from an arbitrarily warped accretion disc, illuminated from above and below by hard X-ray sources. This substantially generalizes previous calculations of reprocessing by accretion discs by including non-axisymmetric effects. We include a relativistic treatment of shadowing by ray-tracing photon paths along Schwarzschild geodesics. We apply this method to two classes of warped discs, and generate a selection of resulting line profiles. New profile features include a time-varying line profile if the warp precesses about the disc, profile differences between 'twisted' and 'twist-free' warps and the possibility of steeper red and softer blue fall-offs than for flat discs. We discuss some qualitative implications of the line profiles in the context of Type I and II Seyfert AGN and other sources.  相似文献   

14.
In this paper, we consider the process of alignment of a spinning black hole and a surrounding misaligned accretion disc. We use a simplified set of equations, that describe the evolution of the system in the case where the propagation of warping disturbances in the accretion disc occurs diffusively, a situation likely to be common in the thin discs in active galactic nuclei (AGN). We also allow the direction of the hole spin to move under the action of the disc torques. In such a way, the evolution of the hole–disc system is computed self-consistently. We consider a number of different situations and we explore the relevant parameter range, by varying the location of the warp radius R w and the propagation speed of the warp. We find that the dissipation associated with the twisting of the disc results in a large increase in the accretion rate through the disc, so that AGN accreting from a misaligned disc are likely to be significantly more luminous than those accreting from a flat disc. We compute explicitly the time-scales for the warping of the disc and for the alignment process and compare our results with earlier estimates based on simplified steady-state solutions. We also confirm earlier predictions that, under appropriate circumstances, accretion can proceed in a counter-aligned fashion, so that the accreted material will spin-down the hole, rather than spinning it up. Our results have implication in a number of different observational features of AGN such as the orientation and shape of jets, the shape of X-ray iron lines and the possibility of obscuration and absorption of X-ray by the outer disc as well as the general issue of the spin history of black holes during their growth.  相似文献   

15.
We have undertaken an extensive study of X-ray data from the accreting millisecond pulsar XTE J1751 − 305 observed by RXTE and XMM–Newton during its 2002 outburst. In all aspects this source is similar to the prototypical millisecond pulsar SAX J1808.4 − 3658, except for the higher peak luminosity of 13 per cent of Eddington, and the optical depth of the hard X-ray source, which is larger by a factor ∼2. Its broad-band X-ray spectrum can be modelled by three components. We interpret the two soft components as thermal emission from a colder  ( kT ∼ 0.6 keV)  accretion disc and a hotter (∼1 keV) spot on the neutron star surface. We interpret the hard component as thermal Comptonization in plasma of temperature ∼40 keV and optical depth ∼1.5 in a slab geometry. The plasma is heated by the accretion shock as the material collimated by the magnetic field impacts on to the surface. The seed photons for Comptonization are provided by the hotspot, not by the disc. The Compton reflection is weak and the disc is probably truncated into an optically thin flow above the magnetospheric radius. Rotation of the emission region with the star creates an almost sinusoidal pulse profile with an rms amplitude of 3.3 per cent. The energy-dependent soft phase lags can be modelled by two pulsating components shifted in phase, which is naturally explained by a different character of emission of the optically thick spot and optically thin shock combined with the action of the Doppler boosting. The observed variability amplitude constrains the hotspot to lie within 3°–4° of the rotational pole. We estimate the inner radius of the optically thick accreting disc to be about 40 km. In that case, the absence of emission from the antipodal spot, which can be blocked by the accretion disc, gives the inclination of the system as ≳70°.  相似文献   

16.
We present X-ray/ γ -ray spectra of Cyg X-1 observed during the transition from the hard to the soft state and in the soft state by ASCA , RXTE and CGRO /OSSE in 1996 May and June. The spectra consist of a dominant soft component below ∼2 keV and a power-law-like continuum extending to at least ∼800 keV. We interpret them as emission from an optically thick, cold accretion disc and from an optically thin, non-thermal corona above the disc. A fraction f ≳0.5 of total available power is dissipated in the corona.
We model the soft component by multicolour blackbody disc emission taking into account the torque-free inner-boundary condition. If the disc extends down to the minimum stable orbit, the ASCA RXTE data yield the most probable black hole mass of M X≈10 M⊙ and an accretion rate,     , locating Cyg X-1 in the soft state in the upper part of the stable, gas-pressure-dominated, accretion-disc solution branch.
The spectrum of the corona is well modelled by repeated Compton scattering of seed photons from the disc off electrons with a hybrid, thermal/non-thermal distribution. The electron distribution can be characterized by a Maxwellian with an equilibrium temperature of kT e∼30–50 keV, a Thomson optical depth of τ ∼0.3 and a quasi-power-law tail. The compactness of the corona is 2≲ℓh≲7, and a presence of a significant population of electron–positron pairs is ruled out.
We find strong signatures of Compton reflection from a cold and ionized medium, presumably an accretion disc, with an apparent reflector solid angle, Ω/2π∼0.5–0.7. The reflected continuum is accompanied by a broad iron K α line.  相似文献   

17.
The broad X-ray iron line, detected in many active galactic nuclei, is likely to be produced by fluorescence from the X-ray-illuminated central parts of an accretion disc close to a supermassive black hole. The time-averaged shape of the line can be explained most naturally by a combination of special and general relativistic effects. Such line profiles contain information about the black hole spin and the accretion disc, as well as the geometry of the emitting region, and may help to test general relativity in the strong gravity regime. In this paper we embark on the computation of the temporal response of the line to the illuminating flux. Previous studies concentrated on the calculation of reverberation signatures from static sources illuminating the disc. In this paper we focus on the more physically justified case of flares located above the accretion disc and corotating with it. We compute the time-dependent iron line, taking into account all general relativistic effects, and show that its shape is of a very complex nature, and we also present light curves accompanying the iron line variability. We suggest that present and future X-ray satellites like XMM or Constellation-X may be capable of detecting features present in the computed reverberation maps.  相似文献   

18.
Using a Monte Carlo method, we derive spectra arising from Comptonization taking place close to a Kerr black hole. We consider a model consisting of a hot thermal corona Comptonizing seed photons emitted by a cold accretion disc. We find that general relativistic effects are crucial for the emerging spectra in models, which involve significant contribution of radiation produced in the black hole ergosphere. As a result of this contribution, spectra of hard X-ray emission produced in the vicinity of a rapidly rotating black hole strongly depend on the inclination of the line of sight, with larger inclinations corresponding to harder spectra. Remarkably, such anisotropy could be responsible for properties of the X-ray spectra of Seyfert galaxies, which appear to be intrinsically harder in type 2 objects than in type 1, as reported recently.  相似文献   

19.
We report on a 50-ks observation of the bright Seyfert 1 galaxy MCG–6-30-15 with the Rossi X-ray Timing Explorer . The data clearly show the broad fluorescent iron line (equivalent width ∼ 250 eV) and the Compton reflection continuum at higher energies. A comparison of the iron line and the reflection continuum has enabled us to constrain the reflective fraction and the elemental abundances in the accretion disc. Temporal studies provide evidence that spectral variability is a result of changes in both the amount of reflection seen and the properties of the primary X-ray source itself.  相似文献   

20.
We have calculated the relativistic reflection component of the X-ray spectra of accretion disks in active galactic nuclei (AGN). Our calculations have shown that the spectra can be significantly modified by the motion of the accretion flow, and the gravity and rotation of the central black hole. The absorption edges in the spectra suffer severe en- ergy shifts and smearing, and the degree of distortion depends on the system parameters, in particular, the inner radius of the accretion disk and the disk viewing inclination angles. The effects are significant. Fluorescent X-ray emission lines from the inner accretion disk could be a powerful diagnostic of space-time distortion and dynamical relativistic effects near the event horizons of accreting black holes. However, improper treatment of the re- flection component in fitting the X-ray continuum could give rise to spurious line-like features. These features mimic the true fluorescent emission lines and may mask their relativistic signatures. Fully relativistic models for reflection continua together with the emission lines are needed in order to extract black-hole parameters from the AGN X-ray spectra.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号