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 125 毫秒
1.
The X‐ray spectra of Active Galactic Nuclei (AGN) are complex and vary rapidly in time as seen in recent observations. Magnetic flares above the accretion disk can account for the extreme variability of AGN. They also explain the observed iron Kα fluorescence lines. We present radiative transfer modeling of the X‐ray reflection due to emission from magnetic flares close to the marginally stable orbit. The hard X‐ray primary radiation coming from the flare source illuminates the accretion disk. A Compton reflection/reprocessed component coming from the disk surface is computed for different emission directions. We assume that the density structure remains adjusted to the hydrostatic equilibrium without external illumination because the flare duration is only a quarter‐orbit. The model takes into account the variations of the incident radiation across the hot spot underneath the flare source. The integrated spectrum seen by a distant observer is computed for flares at different orbital phases close to the marginally stable orbit of a Schwarzschild black hole and of a maximally rotating Kerr black hole. The calculations include relativistic and Doppler corrections of the spectra using a ray tracing technique. We explore the practical possibilities to map out the azimuthal irradiation pattern of the inner accretion disks and conclude that the next generation of X‐ray satellites should reveal this structure from iron Kα line profiles and X‐ray lightcurves. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
Iron line emission is common in the X‐ray spectra of accreting black holes. When the line emission is broad or variable then it is likely to originate from close to the black hole. X‐ray irradiation of the accretion flow by the power‐law X‐ray continuum produces the X‐ray ‘reflection’ spectrum which includes the iron line. The shape and variability of the iron lines and reflection can be used as a diagnostic of the radius, velocity and nature of the flow. The inner radius of the dense flow corresponds to the innermost stable circular orbit and thus can be used to determine the spin of the black hole. Studies of broad iron lines and reflection spectra offer much promise for understanding how the inner parts of accretion flows (and outflows) around black holes operate. There remains great potential for XMM‐Newton to continue to make significant progress in this work. The need for high quality spectra and thus for long exposure times is paramount. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
We report on the iron Kα line properties of a sample of Seyfert galaxies observed with the XMM‐Newton EPIC pn instrument. Using a systematic and uniform analysis, we find that complexity at iron‐K is extremely common in the XMM‐Newton spectra. Once appropriate soft X‐ray absorption, narrow 6.4 keV emission and associated Compton reflection are accounted for, ∼75% of the sample show an improvement when a further component is introduced. The typical properties of the broad emission are both qualitatively and quantitatively consistent with previous results from ASCA. The complexity is in general very well described by relativistic accretion disk models. In most cases the characteristic emission radius is constrained to be within ∼50R g, where strong gravitational effects become important. We find in about 1/3 of the sample the accretion disk interpretation is strongly favoured over competing models. In a few objects no broad line is apparent. We find evidence for emission within 6R g in only two cases, both of which exhibit highly complex absorption. Evidence for black hole spin based on the X‐ray spectra therefore remains tentative. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
We present monitoring analysis of 8 XMM‐Newton observations of the Seyfert 2 galaxy Mrk 3, spanning a period of ∼19 months. The continuum flux in the 3–12 keV band remains constant during this observing period. The X‐ray spectrum is well described, in agreement with previous works, by a highly absorbed (N H > 1024 cm–2) power law model, with a photon index Γ = 1.9 and a strong reflection component. A strong Fe Kα line at 6.4 keV with an equivalent width of ∼500 eV is detected in the X‐ray spectrum. When we consider the co‐added spectrum we also detect a weaker emission line at 7.4 keV corresponding to neutral Ni Kα emission and weak evidence for the presence of an ionized Fe Kα line at 6.7 keV. Direct comparison with the results obtained from an earlier XMM‐Newton observation of Mrk 3, shows a decrease in the continuum flux of ∼30 per cent followed by a similar decrease in the reflected component. Both emission line components at 6.4 and 6.7 keV do not vary. However we find that an alternative model where the N H varies by 20 per cent is also plausible. In this case both the continuum and the reflected emission do not change. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
We have identified three possible ways in which future XMM‐Newton observations can provide significant constraints on the equation of state of neutron stars. First, using a long observation of the neutron star X‐ray transient Cen X‐4 in quiescence one can use the RGS spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X‐ray spectral fitting of the pn and MOS spectra and allows us to investigate whether the variability observed in the quiescent X‐ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in NH. This will test whether the soft thermal spectral component can indeed be due to the hot thermal glow of the neutron star. Potentially such an observation could also reveal redshifted spectral lines from the neutron star surface. Second, XMM‐Newton observations of radius expansion type I Xray bursts might reveal redshifted absorption lines from the surface of the neutron star. Third, XMM‐Newton observations of eclipsing quiescent low‐mass X‐ray binaries provide the eclipse duration. With this the system inclination can be determined accurately. The inclination determined from the X‐ray eclipse duration in quiescence, the rotational velocity of the companion star and the semi‐amplitude of the radial velocity curve determined through optical spectroscopy, yield the neutron star mass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
Initial results on the iron K‐shell line and reflection component in several AGN observed as part of the Suzaku Guaranteed Time program are reviewed. This paper discusses a small sample of Compton‐thin Seyferts observed to date with Suzaku; namely MCG‐5‐23‐16, MCG‐6‐30‐15, NGC4051, NGC3516, NGC2110, 3C 120 and NGC2992. The broad iron Kα emission line appears to be present in all but one of these Seyfert galaxies, while the narrow core of the line from distant matter is ubiquitous in all the observations. The iron line in MCG‐6‐30‐15 shows the most extreme relativistic blurring of all the objects, the red‐wing of the line requires the inner accretion disk to extend inwards to within 2.2R g of the black hole, in agreement with the XMM‐Newton observations. Strong excess emission in the Hard X‐ray Detector (HXD) above 10 keV is observed in many of these Seyfert galaxies, consistent with the presence of a reflection component from reprocessing in Compton‐thick matter (e.g. the accretion disk). Only one Seyfert galaxy (NGC 2110) shows neither a broad iron line nor a reflection component. The spectral variability of MCG‐6‐30‐15, MCG‐5‐23‐16 and NGC 4051 is also discussed. In all 3 cases, the spectra appear harder when the source is fainter, while there is little variability of the iron line or reflection component with source flux. This agrees with a simple two component spectral model, whereby the variable emission is the primary power‐law, while the iron line and reflection component remain relatively constant. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
The X‐ray spectra of luminous Seyfert 1 galaxies often appear to be reflection dominated. In a number of Narrow Line Seyfert 1 (NLS1) galaxies and galactic black holes in the very high state, the variability of the continuum and of the iron line are decoupled, the reflected component being often much less variable than the continuum. These properties have been interpreted as effects of gravitational light bending. In this framework, we present detailed Monte‐Carlo simulations of the reflection continuum in the Kerr metric. These calculations confirm that the spectra and variability behaviour of these sources can be reproduced by the light bending model. As an alternative to the light bending model, we show that similar observational properties are expected from radiation pressure dominated discs subject to violent clumping instabilities and, as a result, have a highly inhomogeneous two‐phase structure. In this model, most of the observed spectral and variability features originate from the complex geometrical structure of the inner regions of near‐Eddington accretion flows and are therefore a signature of accretion physics rather than general relativity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
Luminosity functions are one of the most important observational clues when studying galaxy evolution over cosmic time. In this paper we present the X‐ray luminosity functions for X‐ray detected AGN in the SXDS and GWS fields. The limiting fluxes of our samples are 9.0 ×10–15 and 4.8 ×10–16 erg cm–2 s–1 in the 0.5–7.0 keV band in the two fields, respectively. We carried out analysis in three X‐ray bands and in two redshift intervals up to z ≤ 1.4. Moreover, we derive the luminosity functions for different optical morphologies and X‐ray types. We confirm strong luminosity evolution in all three bands, finding the most luminous objects at higher redshift. However, no signs of density evolution are found in any tested X‐ray band. We obtain similar results for compact and early‐type objects. Finally, we observe the “Steffen effect”, where X‐ray type‐1 sources are more numerous at higher luminosities in comparison with type‐2 sources. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
We present results from a recent broad‐band monitoring in optics of the Seyfert 1 type galaxy Mrk 279. We build and analyse the BV RI light curve covering a period of seven years (1995–2002). We also show some evidence for the existence of two different states in brightness and suggest, based on a modelling of the optical continuum, that these states may result from transition between a thin disk and an ADAF accretion modes. We assume that the short‐term variability is due to a reprocessing of a variable X‐ray emission from an inner ADAF part of the flow, while the long‐term one may be a result from a change of the transition radius. Our tests show a good match with the observations for a reasonable set of accretion parameters, close to the expected ones for Mrk 279. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
We present the results of the simultaneous XMM‐Newton and Chandra observations of the bright Seyfert 1.9 galaxy MCG–5‐23‐16, which is one of the best known examples of a relativistically broadened iron Kα line. We find that: a) the soft X‐ray emission is likely to be dominated by photoionized gas, b) the complex iron emission line is best modelled with a narrow and a broad component with a FWHM ∼44000 km/s. This latter component has an EW ∼50 eV and its profile is well described with an emission line mainly originating from the accretion disk a few tens of gravitational radii from the central black hole and viewed with an inclination angle ∼40°. We found evidence of a possible sporadic absorption line at ∼7.7 keV which, if associated with Fe XXVI Kα resonance absorption, is indicative of a possible high velocity (v ∼ 0.1c) outflow. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
Gamma‐ray bursts (GRBs) are the most powerful explosions since the formation of the Universe, associated with the death of massive stars or mergers of compact stellar objects. Several recent striking results strongly support the idea that host galaxies of GRBs are opening a new view on our understanding of galaxy formation and evolution, back to the very primordial universe at z ∼ 8. They form a unique sample of galaxies which cover a wide range of redshift, they are typically weak with low mass and unlike other methods they are not selected on luminosity. In recent years, thanks to the support of new generation instruments, multi‐band photometry and spectroscopy allow us to better investigate the properties of these host galaxies (e.g., stellar mass, age, SFR, metallicity), to study their possible evolution and to compare them with field galaxies and other classes of galaxies. GRB host spectroscopy is one of the main science drivers behind the X‐shooter spectrograph. In this paper, we present the first results of the program devoted to Italian‐French GTO multiband spectroscopy of GRB host galaxies with X‐shooter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
We present the analysis of optical and X‐ray XMM‐Newton data of the source 4U 1344‐60. On the basis of the optical data we propose to classify 4U 1344‐60 as a Seyfert 1.5 galaxy and we measured a redshift value z = 0.012 ± 0.001. The observed X‐ray spectrum is complex. The continuum emission can be described as a power law obscured by two neutral absorption components. 4U 1344‐60 exhibits a broad and skewed iron line at 6.4 keV most likely originated in a few gravitational radius of an accretion disc. The analysis also reveals the presence of two narrow emission line‐like features at ∼4.9 keV and ∼5.3 keV. Assuming that hot spots on the surface of the accretion disc, orbiting very close to the black hole is responsible of these emission lines, the accretion disc would present an inclination of 20° and the active regions would be located in the 6–10 R g radius range. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
This paper shows that our understanding of the statistical properties of X‐ray selected normal galaxies (e.g. X‐ray luminosity function) can be significantly improved by combining a wide‐area XMM‐Newton survey with the moderare resolution and high S/N optical spectroscopy of the SDSS. Such a combined dataset has the potential to minimise uncertainties that affect existing normal galaxy samples at X‐rays, such as small number statistics, cosmic variance, AGN contamination and incompleteness at bright X‐ray luminosities. It is demonstrated that a 100 deg2 XMM‐Newton survey in the SDSS area to the limit fX(0.5–2 keV) ≈ 5 × 10–15 erg cm–2 s–1 will detect over 400 X‐ray selected normal galaxies with excellent control over systematic biases, thereby providing tight contraints on the X‐ray luminosity function at z ≈ 0.1. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
First studies of the X‐ray source population of M 31 were performed with the Einstein Observatory and ROSAT. High resolution Chandra Observatory images not only spatially resolved the center area but also supernova remnants (SNRs) in the galaxy. Source catalogues of restricted areas were presented with high astrometric accuracy. Also luminosity function studies and studies of individual sources based on Chandra and XMM‐Newton observations led to a better knowledge of the X‐ray source population. An XMM‐Newton source catalog based on archival observations revealed more than 850 sources down to a 0.2–4.5 keV luminosity of 1035 erg s–1. EPIC hardness ratios as well as informations from earlier X‐ray, optical, and radio catalogues were used to distinguish between different source classes (SNRs, supersoft sources (SSSs), X‐ray binaries (XRBs), globular cluster sources within M 31, and foreground stars and objects in the background). However, many sources could only be classified as “hard”. These sources may either be XRBs or Crab‐like SNRs in M 31 or background sources. Two of the globular cluster sources could be identified as low mass XRBs with a neutron star as compact object as they showed type I X‐ray bursts. Many of the SSSs were identified as optical novae. Inspired by these results an XMM‐Newton survey of the entire D25 disk of M 31 and a dedicated program to monitor X‐ray counterparts of optical novae in M 31 was started. We discuss implications for further nearby galaxy studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
We present a spatial analysis of the soft X‐ray and Hα emissions from the outflow of the starburst galaxy M82. We find that the two emissions are tightly correlated on various scales. The O VII triplet of M82, as resolved by X‐ray grating observations of XMM‐Newton, is dominated by the forbidden line, inconsistent with the thermal prediction. The O VII triplet also shows some spatial variations. We discuss three possible explanations for the observed O VII triplet, including the charge exchange at interfaces between the hot outflow and neutral cool gas, a collisional non‐equilibrium‐ionization recombining plasma, and resonance scattering (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
We consider the contribution of microlensing to the AGN Fe Kα line and X‐ray continuum amplification and variation. To investigate the variability of the line and X‐ray continuum, we studied the effects of microlensing on quasar X‐ray spectra produced by crossing of a microlensing pattern across a standard relativistic accretion disk. To describe the disk emission we used a ray tracing method considering both metrics, Schwarzschild and Kerr. We found that the Fe Kα and continuum may experience significant amplification by a microlensing event (even for microlenses of very small mass). Also, we investigate a contribution of microlensing to the X‐ray variability of high‐redshifted QSOs, finding that cosmologically distributed deflector may contribute significantly to the X‐ray variability of high‐redshifted QSOs (z > 2). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
Current, accumulating evidence for (mildly) relativistic blue‐ and red‐shifted absorption lines in AGNs is reviewed. XMM‐Newton and Chandra sensitive X‐ray observations are starting to probe not only the kinematics (velocity) but also the dynamics (accelerations) of highly ionized gas flowing in‐and‐out from, likely, a few gravitational radii from the black hole. It is thus emphasized that X‐ray absorption‐line spectroscopy provides new potential to map the accretion flows near black holes, to probe the launching regions of relativistic jets/outflows, and to quantify the cosmological feedback of AGNs. Prospects to tackle these issues with future high energy missions are briefly addressed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
Mkn 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM‐Newton for a total cumulated exposure time of ∼108 ks. We present in this paper a broad band spectral analysis of the complete EPIC‐pn data sets. These observations confirm the presence of the strong soft excess and complex iron line profile known to be present in this source since a long time. They also reveal their extreme and puzzling spectral and temporal behaviors. Indeed, the 0.5–2 keV soft X‐ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixed of broad and narrow components, both variable but on different timescales. The broad‐band 0.5–10 keV spectra are well described by a model including a primary power law continuum, a blurred photoionized reflection and a narrow iron line, the blurred reflection fitting self‐consistently the soft excess and the broad line component. The origin and nature of the narrow component is unclear. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
We review some recent results on the identification and characterisation of Active Galactic Nuclei (AGN) obtained by cross correlating X‐ray surveys with infrared and submillimetre surveys. We also look toward the scientific gains that could be achieved from an XMM‐Newton survey of the medium‐deep legacy fields that are being observed at ≈ 1–850 μm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
I review some basic results on AGN with supersoft X‐ray spectra and their relations to Galactic binaries in their soft high states. This paper is based on a talk given at the Supersoft Sources Workshop at ESTEC in May 2009. Given the length of the talk and the number of pages the review cannot be complete and is biased towards my personal view. I demonstrate that at high accretion rates supersoft AGNs and Galactic binaries share steep soft X‐ray spectra, that the X‐ray variability of supersoft AGNs is more pronounced compared to Galactic binaries in their high states, that the X‐ray variability of supersoft novae and supersoft AGNs is similar, and that in Galactic binaries mostly positive time lags are seen, while negative time lags are observed in some supersoft AGN (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  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