Suzaku observation of NGC 3516: complex absorption and the broad and narrow Fe K lines     

A. Markowitz  J. N. Reeves  P. Serlemitsos  T. Yaqoob  H. Awaki  A. Fabian  L. Gallo  R. E. Griffiths  H. Kunieda  G. Miniutti  R. Mushotzky  T. Okajima 《Astronomische Nachrichten》2006,327(10):1087-1090

We present preliminary results from a 150 ks Suzaku observation of the Seyfert 1 galaxy NGC 3516. Suzaku 's wide bandpass has enabled us to deconvolve the broadband emitting and absorbing components in this object, breaking model degeneracies inherent in previous, smaller‐bandpass spectra. The primary power‐law continuum is absorbed by an ionized absorber as well as a partial‐covering absorber; the column density of the ionized absorber has increased by a factor of ∼3 since XMM‐Newton observations in 2001. We detect a soft power‐law component which may be scattered emission. We confirm the presence of the broad Fe line, finding a eV equivalent width line that indicates emission extending down to a few Schwarzschild radii. Models which exclude either the broad line or the partial‐covering absorber are rejected. Suzaku 's high effective area and low background near 6 keV also allow us to resolve the narrow Fe K emission line; we find a FWHM velocity width near 4000 km s^–1, commensurate with Broad Line Region velocities. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The X-ray variability of the Seyfert 1 galaxy MCG–6-30-15 from long ASCA and RXTE observations     

Julia C. Lee  †  A. C. Fabian  Christopher S. Reynolds  ‡  W. N. Brandt  Kazushi Iwasawa 《Monthly notices of the Royal Astronomical Society》2000,318(3):857-874

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An extended multi-zone model for the MCG–6-30-15 warm absorber     

R. Morales  A. C. Fabian  C. S. Reynolds 《Monthly notices of the Royal Astronomical Society》2000,315(1):149-154

The variable warm absorber seen with ASCA in the X-ray spectrum of MCG–6-30-15 shows complex time behaviour in which the optical depth of O  viii anticorrelates with the flux whereas that of O  vii is unchanging. The explanation in terms of a two-zone absorber has since been challenged by BeppoSAX observations. These present a more complicated behaviour for the O  viii edge. We demonstrate here that the presence of a third, intermediate, zone can explain all the observations. In practice, warm absorbers are likely to be extended, multi-zone regions of which only part causes directly observable absorption edges at any given time.  相似文献   

Zw 1718.10108: a highly disturbed galaxy cluster at low Galactic latitude     

K. Iwasawa  S. Ettori  A. C. Fabian  A. C. Edge  H. Ebeling 《Monthly notices of the Royal Astronomical Society》2000,313(3):515-523

We report the discovery of highly distorted X-ray emission associated with the nearby cluster Zw 1718.10108, one of the dominant members of which is the powerful radio galaxy 3C353. This cluster has been missed by previous X-ray cluster surveys because of its low Galactic latitude ( b =19.5°), despite its brightness in the hard X-ray band (210 keV flux of 1.210¹¹ erg cm² s¹). Our optical charge-coupled device image of the central part of the cluster reveals many member galaxies which are dimmed substantially by heavy Galactic extinction. We have measured redshifts of three bright galaxies near the X-ray emission peak and they are all found to be around z =0.028. The ASCA gas imaging spectrometer and ROSAT high-resolution imager images show three aligned X-ray clumps embedded in low surface-brightness X-ray emission extended by 30 arcmin. The averaged temperature measured with ASCA is kT =4.3±0.2 keV, which appears to be hot for the bolometric luminosity when compared with the temperatureluminosity correlation of galaxy clusters. The irregular X-ray morphology and evidence for a non-uniform temperature distribution suggest that the system is undergoing a merger of substructures. Since the sizes and luminosities of the individual clumps are consistent with those of galaxy groups, Zw 1718.10108 is interpreted as an on-going merger of galaxy groups in a dark matter halo forming a cluster of galaxies and thus is in a transition phase of cluster formation.  相似文献   

Magnetic flares and the optical variability of the X-ray transient XTE J1118+480     

A. Merloni  T. Di Matteo †  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2000,318(1):L15-L19

The simultaneous presence of a strong quasi-periodic oscillation, of period ∼10 s, in the optical and X-ray light curves of the X-ray transient XTE J1118+480 suggests that a significant fraction of the optical flux originates from the inner part of the accretion flow, where most of the X-rays are produced. We present a model of magnetic flares in an accretion disc corona where thermal cyclo-synchrotron emission contributes significantly to the optical emission, while the X-rays are produced by inverse Compton scattering of the soft photons produced by dissipation in the underlying disc and by the synchrotron process itself. Given the observational constraints, we estimate the values for the coronal temperature, optical depth and magnetic field intensity, as well as the accretion rate for the source. Within our model we predict a correlation between optical and hard X-ray variability and an anticorrelation between optical and soft X-rays. We also expect optical variability on flaring time-scales (∼tens of ms), with a power-density spectrum similar to that observed in the X-ray band. Finally, we use both the available optical/extreme-ultraviolet/X-ray spectral energy distribution and the low-frequency time variability to discuss limits on the inner radius of the optically thick disc.  相似文献   

The ROSAT Brightest Cluster Sample – IV. The extended sample     

H. Ebeling  A. C. Edge  S. W. Allen  C. S. Crawford  A. C. Fabian  J. P. Huchra 《Monthly notices of the Royal Astronomical Society》2000,318(2):333-340

We present a low-flux extension of the X-ray-selected ROSAT Brightest Cluster Sample (BCS) published in Paper I of this series. Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere ( δ ≥0°) and at high Galactic latitudes (| b |≥20°). It comprises 99 X-ray-selected clusters of galaxies with measured redshifts z ≤0.3 (as well as eight more at z >0.3) and total fluxes between 2.8×10⁻¹² and 4.4×10⁻¹² erg cm⁻² s⁻¹ in the 0.1–2.4 keV band (the latter value being the flux limit of the original BCS). The extension can be combined with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the RASS to date.
The nominal completeness of the combined sample (defined with respect to a power-law fit to the bright end of the BCS log  N –log  S distribution) is relatively low at 75 per cent (compared with 90 per cent for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift.
In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray-bright clusters in the northern hemisphere which we hope will prove useful in the preparation of cluster observations with the next generation of X-ray telescopes such as Chandra and XMM-Newton .
An electronic version of the eBCS can be obtained from the following URL: http://www.ifa.hawaii.edu/~ebeling/clusters/BCS.html.  相似文献   

The (ir)relevance of transaction costs in climate policy instrument choice: an analysis of the EU and the US     

Fabian Joas  Christian Flachsland 《Climate Policy》2016,16(1):26-49

This article assesses the relevance of ex post transaction costs in the choice of climate policy instruments in the EU (focusing mainly on the example of Germany) and the US. It reviews all publicly available empirical ex post transaction cost studies of climate policy instruments broken down by the main private and public sector cost factors and offers hypotheses on how these factors may scale depending on instrument design and other contextual factors. The key finding from the evaluated schemes is that it is possible to reject the hypothesis that asymmetries in ex post transaction costs across instruments are large and, thus, play a pivotal role in climate policy instrument choice. Both total and relative ex post transaction costs can be considered low. This conjecture differs from the experience in other areas of environmental policy instruments where high total transaction costs are considered to be important factors in the overall assessment of optimal environmental policy choice. Against this background, the main claim of this article is that in climate policy instrument choice, ex post transaction cost considerations play a minor role in large countries that feature similar institutional characteristics as the EU and the US. Rather, the focus should be on the efficiency properties of instruments for incentivizing abatement, as well as equity and political economy considerations (and other societally relevant objectives). In order to inform transaction cost considerations in climate policy instrument choice in countries that adopt new climate policies, more data would be desirable in order to enable more robust estimates of design- and context-specific transaction-cost scaling factors.

Policy relevance

The findings of this study can help inform policy makers who plan to set up novel climate policy instruments. The results indicate that ex post transaction costs play a minor role for large countries that feature similar institutional characteristics as the EU and the US. For instrument design the focus should rather be on efficiency properties of instruments in incentivizing abatement, as well as equity and political economy considerations (and other societally relevant objectives).  相似文献   

The TurbEFA Field Experiment—Measuring the Influence of a Forest Clearing on the Turbulent Wind Field     

Ronald Queck  Christian Bernhofer  Anne Bienert  Fabian Schlegel 《Boundary-Layer Meteorology》2016,160(3):397-423

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Sur les Équations approchées de la Dynamique atmosphérique     

P. Dedecker 《Meteorology and Atmospheric Physics》1950,2(2-3):223-238

Résumé Les équations approchées de la dynamique atmosphérique ne sont valables que dans un certain domaine entourant l'origine des coordonnées et dont nous calculons l'ordre de grandeur. En ce qui concerne les équations (5) utilisées habituellement par les météorologistes, son rayon horizontal est à peine de l'ordre de la dizaine de mètres. Par contre ce rayon est de l'ordre de 500 kilomètres pour les équations (6) et il en est de même pour les équations (7) qui sont adaptées à l'étude des cartes des surfaces isobares. Ce résultat peut paraître paradoxal puisque l'on passe habituellement de (5) à (7) en utilisant une forme approchée () du géopotentiel; il se fait que l'on obtient les mêmes équations (7) à partir de (6) en utilisant la forme exacte du géopotentiel (théorème I).Les équations approchées (9) ont une forme très voisine de (5) et sont adaptées à l'étude des cartes des surfaces équi-géopotentielles. On peut également les déduire de (6) en utilisant la forme exacte du géopotentiel (théorème II).L'origine mathématique de ces propositions réside dans une propriété d'un 3-vecteur covariant vis à vis des changements de coordonnées (14); on voit en même temps que les théorèmes I et II sont des cas particuliers d'un théorème plus général (théorème III).Nous considérons ensuite d'autres transformations de coordonnées qui ne modifient que très légèrement les équations approchées (théorèmes IV et V).

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Summary The approximated equations of atmospheric dynamics are valid only within a certain region surrounding the origin of the coordinates of which the order of magnitude is calculated. Concerning equations (5) which are usually employed in meteorology, their horizontal radius reaches hardly the magnitude of 10 meters. On the other hand this radius amounts to the magnitude of 500 kilometers with equations (6) and equally with (7) which are adapted for the study of charts of isobaric surfaces. This result may seem paradoxical because usually formulae (7) are deduced from (5) by employing an approximated form () of the geopotential; but in using the exact form of the geopotential, equations (7) are obtained from (6) (theorem I). The approximated equations (9) have a very similar form as (5) and are especially adapted for the study of the charts of equi-geopotential surfaces; using the exact form of the geopotential they can also be derived from (6) (theorem II).The mathematical origin of these facts lies upon a quality of a 3-vector which is covariant against the coordinate transformations (14); furthermore it can be shown that the theorems I and II are special cases of a more general theorem (theorem III). Finally, other transformations of coordinates are discussed, through which the approximated equations are modified only insignificantly (theorems IV and V).

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Zusammenfassung Die genäherten Gleichungen der atmosphärischen Dynamik sind nur in einem bestimmten Gebiet um den Koordinatenursprung gültig, dessen Größenordnung berechnet wird; für die Gleichungen (5), die in der Meteorologie gewöhnlich benützt werden, erreicht sein horizontaler Radius kaum die Größenordnung von 10 m. Demgegenüber ist der Radius für die Gleichungen (6) von der Größenordnung von 500 km und ebenfalls für die Gleichungen (7), die sich für das Studium der Karten der Isobarenflächen eignen. Dieses Resultat mag überraschend erscheinen, da man gewöhnlich unter Benützung einer genäherten Form () des Geopotentials von (5) zu (7) Übergeht; geht man jedoch von der exakten Form des Geopotentials aus, so erhält man die Gleichungen (7) aus (6) (Theorem I). Die genäherten Gleichungen (9) haben eine sehr ähnliche Form wie (5) und eignen sich besonders für das Studium der Karten der äqui-geopotentiellen Flächen; unter Benützung der exakten Form des Geopotentials lassen sie sich ebenfalls aus (6) ableiten (Theorem II).Der mathematische Ursprung dieser Tatsachen beruht auf einer Eigenschaft eines 3-Vektors, der gegenüber den Koordinatentransformationen (14) kovariant ist; ferner kann man zeigen, daß die Theoreme I und II Spezialfälle eines allgemeineren Theorems sind (Theorem III). Außerdem werden noch andere Koordinatentransformationen untersucht, durch die die genäherten Gleichungen nur geringfügig verändert werden (Theoreme IV und V).

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Avec 1 figure.  相似文献   

The Bremen ocean bottom tiltmeter (OBT) – a technical article on a new instrument to monitor deep sea floor deformation and seismicity level     

Marcus Fabian  Heinrich Villinger 《Marine Geophysical Researches》2007,28(1):13-26

The Bremen ocean bottom tiltmeter is a new 6000 m-depth deep sea instrument for autonomous observation of sea floor tilt with signal periods longer than 7.5 s. The instrument also records vertical acceleration in the frequency range from DC to 1 Hz. The tiltmeter has an Applied Geomechanics Inc. 756 wide angle biaxial bubble tilt sensor with a resolution of 1.0μ rad (0.2 arc second). A Kistler Corp. MEMS accelerometer of type Servo K-Beam 8330A2.5 with about 10⁻⁵m/s² resolution is used for the acceleration measurements. An Oceanographic Embedded Systems AD24 24 bit Sigma-Delta converter, which is controlled by a low-power Persistor Inc. embedded computer system of type CF 2, samples the data. The duration of tiltmeter operation is more than one year, which is controlled by the battery life. In our design the tiltmeter does not need active leveling devices, i.e., servo motors or other moving components to adjust sensors or frame. We designed the instrument for deployments by means of a remote operated vehicle. Since May 2005 the Bremen ocean bottom tiltmeter has recorded sea floor deformation and seismicity level in the Logatchev hydrothermal vent field, Mid-Atlantic Ridge. The tiltmeter is a part of the monitoring system of project ‘Logatchev Long-Term Environmental Monitoring,’ called LOLEM, of the German research program with the name ‘Schwerpunktprogramm 1144: Vom Mantel zum Ozean.’  相似文献