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  • 1
    Electronic Resource
    Electronic Resource
    The signature of supernova ejecta in the X-ray afterglow of the γ-ray burst 011211 (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 416 (2002), S. 512-515 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Now that γ-ray bursts (GRBs) have been determined to lie at cosmological distances, their isotropic burst energies are estimated to be as high as 1054 erg (ref. 2), making them the most energetic phenomena in the Universe. The nature of the progenitors ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/416512a
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    Paper (German National Licenses)
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  • 2
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    The Chandra/HETG view of NGC 1365 in a Compton-thick state (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: We present the analysis of a Chandra High-Energy Transmission Grating (HETG) observation of the local Seyfert galaxy NGC 1365. The source, well known for its dramatic X-ray spectral variability, was caught in a reflection-dominated, Compton-thick state. The high spatial resolution afforded by Chandra allowed us to isolate the soft X-ray emission from the active nucleus, neglecting most of the contribution from the kpc-scale starburst ring. The HETG spectra thus revealed a wealth of He- and H-like lines from photoionized gas, whereas in larger aperture observations these are almost exclusively produced through collisional ionization in the circumnuclear environment. Once the residual thermal component is accounted for, the emission-line properties of the photoionized region close to the hard X-ray continuum source indicate that NGC 1365 has some similarities to the local population of obscured active galaxies. In spite of the limited overall data quality, several soft X-ray lines seem to have fairly broad profiles (~800–1300 km s –1 full width at half-maximum), and a range of outflow velocities (up to ~1600 km s –1 , but possibly reaching a few thousand km s –1 ) appears to be involved. At higher energies, the Kα fluorescence line from neutral iron is resolved with 〉99 per cent confidence, and its width of ~3000 km s –1 points to an origin from the same broad-line region clouds responsible for eclipsing the X-ray source and likely shielding the narrow-line region.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    The Suzaku view of highly ionized outflows in AGN - II. Location, energetics and scalings with bolometric luminosity (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-02
    Description: Ongoing studies with XMM–Newton have shown that powerful accretion disc winds, as revealed through highly ionized Fe K-shell absorption at E  ≥ 6.7 keV, are present in a significant fraction of active galactic nuclei (AGNs) in the local Universe (Tombesi et al. 2010a ). In Gofford et al., we analysed a sample of 51 Suzaku -observed AGNs and independently detected Fe K absorption in ~40 per cent of the sample, and we measured the properties of the absorbing gas. In this work, we build upon these results to consider the properties of the associated wind. On average, the fast winds ( v w  〉 0.01 c ) are located 〈 r 〉 ~ 10 15–18  cm (typically ~10 2–4 r s ) from their black hole, their mass outflow rates are of the order of $\langle \skew{3}\dot{M}_{\rm w}\rangle \sim 0.01\hbox{--}1$  M  yr –1 or ${\sim }(0.01\hbox{--}1)\skew{3}\dot{M}_{\rm Edd}$ and kinetic power is constrained to 〈 L w 〉 ~ 10 43–45  erg s –1 , equivalent to ~(0.1–10 per cent) L Edd . We find a fundamental correlation between the source bolometric luminosity and the wind velocity, with $v_{\rm w} \propto L_{\rm bol}^{\alpha }$ and $\alpha =0.4^{+0.3}_{-0.2}$ (90 per cent confidence), which indicates that more luminous AGN tend to harbour faster Fe K winds. The mass outflow rate $\skew{3}\dot{M}_{\rm w}$ , kinetic power L w and momentum flux $\dot{p}_{\rm w}$ of the winds are also consequently correlated with L bol , such that more massive and more energetic winds are present in more luminous AGN. We investigate these properties in the framework of a continuum-driven wind, showing that the observed relationships are broadly consistent with a wind being accelerated by continuum-scattering. We find that, globally, a significant fraction (~85 per cent) of the sample can plausibly exceed the L w / L bol  ~ 0.5 per cent threshold thought necessary for feedback, while 45 per cent may also exceed the less conservative ~5 per cent of L bol threshold as well. This suggests that the winds may be energetically significant for AGN–host-galaxy feedback processes.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    X-ray timing analysis of the quasar PG 1211+143 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-21
    Description: We report on a timing analysis of a new ~630 ks XMM–Newton observation of the quasar, PG 1211+143. We find a well-defined X-ray power spectrum with a well-detected bend at ~7 x 10 –5 Hz, consistent with the established t bend – M BH correlation for luminous, accreting black holes. We find the linear rms–flux relation commonly observed in accreting black hole systems and investigate the energy-dependence of the rms. The fractional rms is roughly constant with energy on short time-scales (〈1 d; within observations) whereas there is enhanced soft band variability on long time-scales (between observations typically spaced by a few days). Additionally, we also report on the optical–UV variability using the Optical Monitor on-board XMM–Newton and a ~2-month-long overlapping monitoring programme with Swift . We find that, although there is little UV variability within observations (〈1 d), UV variations of a few per cent exist on time-scales of ~days–weeks.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 5
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    The puzzling X-ray continuum of the quasar MR 2251-178 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-15
    Description: We report on a comprehensive X-ray spectral analysis of the nearby radio-quiet quasar MR 2251–178, based on the long-look (~400 ks) XMM–Newton observation carried out in 2011 November. As the properties of the multiphase warm absorber (thoroughly discussed in a recent, complementary work) hint at a steep photoionizing continuum, here we investigate into the nature of the intrinsic X-ray emission of MR 2251–178 by testing several physical models. The apparent 2–10 keV flatness as well as the subtle broad-band curvature can be ascribed to partial covering of the X-ray source by a cold, clumpy absorption system with column densities ranging from a fraction to several x 10 23  cm –2 . As opposed to more complex configurations, only one cloud is required along the line of sight in the presence of a soft X-ray excess, possibly arising as Comptonized disc emission in the accretion disc atmosphere. On statistical grounds, even reflection with standard efficiency off the surface of the inner disc cannot be ruled out, although this tentatively overpredicts the observed ~14–150 keV emission. It is thus possible that each of the examined physical processes is relevant to a certain degree, and hence, only a combination of high-quality, simultaneous broad-band spectral coverage and multi-epoch monitoring of X-ray spectral variability could help disentangling the different contributions. Yet, regardless of the model adopted, we infer for MR 2251–178 a bolometric luminosity of ~5–7 10 45  erg s –1 , implying that the central black hole is accreting at ~15–25 per cent of the Eddington limit.
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    Topics: Physics
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  • 6
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    Short-term X-ray spectral variability of the quasar PDS 456 observed in a low-flux state (2016)
    Oxford University Press
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    Publication Date: 2016-03-17
    Description: We present a detailed analysis of a recent, 2013 Suzaku campaign on the nearby ( z  = 0.184) luminous ( L bol  ~ 10 47 erg s –1 ) quasar PDS 456. This consisted of three observations, covering a total duration of ~1 Ms and a net exposure of 455 ks. During these observations, the X-ray flux was unusually low, suppressed by a factor of 〉10 in the soft X-ray band when compared to previous observations. We investigated the broad-band continuum by constructing a spectral energy distribution (SED), making use of the optical/UV photometry and hard X-ray spectra from the later simultaneous XMM–Newton and NuSTAR campaign in 2014. The high-energy part of this low-flux SED cannot be accounted for by physically self-consistent accretion disc and corona models without attenuation by absorbing gas, which partially covers a substantial fraction of the line of sight towards the X-ray continuum. At least two layers of absorbing gas are required, of column density log ( N H,low /cm –2 ) = 22.3 ± 0.1 and log ( N H,high /cm –2 ) = 23.2 ± 0.1, with average line-of-sight covering factors of ~80 per cent (with typical ~5 per cent variations) and 60 per cent (±10–15 per cent), respectively. During these observations PDS 456 displays significant short-term X-ray spectral variability, on time-scales of ~100 ks, which can be accounted for by variable covering of the absorbing gas along the line of sight. The partial covering absorber prefers an outflow velocity of $v_{\rm pc} = 0.25^{+0.01}_{-0.05}\,c$ at the 〉99.9 per cent confidence level over the case where v pc  = 0. This is consistent with the velocity of the highly ionized outflow responsible for the blueshifted iron K absorption profile. We therefore suggest that the partial covering clouds could be the denser, or clumpy part of an inhomogeneous accretion disc wind. Finally estimates are placed upon the size-scale of the X-ray emission region from the source variability. The radial extent of the X-ray emitter is found to be of the order ~15–20 R g , although the hard X-ray (〉2 keV) emission may originate from a more compact or patchy corona of hot electrons, which is typically ~6–8 R g in size.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Imprints of a high-velocity wind on the soft X-ray spectrum of PG1211+143 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-22
    Description: An extended XMM–Newton observation of the luminous narrow-line Seyfert galaxy PG1211+143 in 2014 has revealed a more complex high-velocity wind, with components distinguished in velocity, ionization level, and column density. Here we report soft X-ray emission and absorption features from the ionized outflow, finding counterparts of both high-velocity components, v  ~ 0.129c and v  ~ 0.066c, recently identified in the highly ionized Fe K absorption spectrum. The lower ionization of the comoving soft X-ray absorbers imply a distribution of higher density clouds embedded in the main outflow, while much higher column densities for the same flow component in the hard X-ray spectra suggest differing sightlines to the continuum X-ray source.
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    Topics: Physics
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  • 8
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    Ultrafast outflows in radio-loud active galactic nuclei (2014)
    Oxford University Press
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    Publication Date: 2014-07-30
    Description: Recent X-ray observations show absorbing winds with velocities up to mildly relativistic values of the order of ~0.1 c in a limited sample of six broad-line radio galaxies. They are observed as blueshifted Fe  xxv–xxvi K-shell absorption lines, similarly to the ultrafast outflows (UFOs) reported in Seyferts and quasars. In this work we extend the search for such Fe K absorption lines to a larger sample of 26 radio-loud active galactic nuclei (AGN) observed with XMM–Newton and Suzaku . The sample is drawn from the Swift Burst Alert Telescope 58-month catalogue and blazars are excluded. X-ray bright Fanaroff–Riley Class II radio galaxies constitute the majority of the sources. Combining the results of this analysis with those in the literature we find that UFOs are detected in 〉27 per cent of the sources. However, correcting for the number of spectra with insufficient signal-to-noise ratio, we can estimate that the incidence of UFOs is this sample of radio-loud AGN is likely in the range f ~= (50 ± 20) per cent. A photoionization modelling of the absorption lines with xstar allows us to estimate the distribution of their main parameters. The observed outflow velocities are broadly distributed between v out 1000 km s –1 and v out ~= 0.4 c , with mean and median values of v out ~= 0.133 c and v out ~= 0.117 c , respectively. The material is highly ionized, with an average ionization parameter of log ~= 4.5 erg s –1  cm, and the column densities are larger than N H  〉 10 22  cm –2 . Overall, these characteristics are consistent with the presence of complex accretion disc winds in a significant fraction of radio-loud AGN and demonstrate that the presence of relativistic jets does not preclude the existence of winds, in accordance with several theoretical models.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 9
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    An outburst scenario for the X-ray spectral variability in 3C 111 (2013)
    Oxford University Press
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    Publication Date: 2013-08-22
    Description: We present a combined Suzaku and Swift BAT broad-band E  = 0.6–200 keV spectral analysis of three 3C 111 observations obtained in 2010. The data are well described with an absorbed power-law continuum and a weak ( R  ~= 0.2) cold reflection component from distant material. We constrain the continuum cutoff at E C  ~= 150–200 keV, which is in accordance with X-ray Comptonization corona models and supports claims that the jet emission is only dominant at much higher energies. Fe xxvi Lyα emission and absorption lines are also present in the first and second observations, respectively. The modelling and interpretation of the emission line is complex and we explore three possibilities. If originating from ionized-disc reflection, this should be emitted at r in  ≥ 50 r g or, in the lamp-post configuration, the illuminating source should be at a height of h  ≥ 30 r g above the black hole. Alternatively, the line could be modelled with a hot collisionally ionized plasma with temperature $kT = 22.0^{+6.1}_{-3.2}$ keV or a photoionized plasma with $\log \xi = 4.52^{+0.10}_{-0.16}$ erg s –1 cm and column density N H  〉 3 10 23 cm –2 . However, the first and second scenarios are less favoured on statistical and physical grounds, respectively. The blueshifted absorption line in the second observation can be modelled as an ultrafast outflow (UFO) with ionization parameter $\log \xi = 4.47^{+0.76}_{-0.04}$ erg s –1 cm, column density $N_\mathrm{H} = (5.3^{+1.8}_{-1.3})\times 10^{22}$ cm –2 and outflow velocity v out  = 0.104 ± 0.006 c . Interestingly, the parameters of the photoionized emission model remarkably match those of the absorbing UFO, supporting the possibility that the same material could be responsible for both emission and absorption. We suggest an outburst scenario in which an accretion disc wind, initially lying out of the line of sight and observed in emission, then crosses our view to the source and it is observed in absorption as a mildly relativistic UFO.
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    Topics: Physics
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  • 10
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    Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers (2013)
    Oxford University Press
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    Publication Date: 2013-03-02
    Description: The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is 〉60 per cent, consistent with previous studies. The fraction of sources with UFOs is 〉34 per cent, 〉67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least ~0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.
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    Topics: Physics
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