8,558 research outputs found
Soft-excess in ULX spectra: disc emission or wind absorption?
We assess the claim that Ultra-luminous X-ray sources (ULXs) host
intermediate-mass black holes (BH) by comparing the cool disc-blackbody model
with a range of other models, namelly a more complex physical model based on a
power-law component slightly modified at various energies by smeared
emission/absorption lines from highly-ionized gas. Our main conclusion is that
the presence of a soft excess, or a soft deficit, depends entirely on the
energy range to which we choose to fit the ``true'' power-law continuum; hence,
we argue that those components should not be taken as evidence for accretion
disc emission, nor used to infer BH masses. We speculate that bright ULXs could
be in a spectral state similar to (or an extension of) the steep-power-law
state of Galactic BH candidates, in which the disc is completely comptonized
and not directly detectable, and the power-law emission may be modified by the
surrounding, fast-moving, ionized gas.Comment: To appear in the proceedings of "The Multicoloured Landscape of
Compact Objects and their Explosive Progenitors: Theory vs. Observations",
Cefalu', Sicily, June 11-24, 2006 (AIP). Compilation needs specific AIP .clo,
.cls, .sty and .tex files (included along with the paper .tex file and
figures
Does magnetic pressure affect the ICM dynamics?
A possible discrepancy found in the determination of mass from gravitational
lensing data, and from X-rays observations, has been largely discussed in the
latest years (for instance, Miralda-Escude & Babul (1995)). Another important
discrepancy related to these data is that the dark matter is more centrally
condensed than the X-ray-emitting gas, and also with respect to the galaxy
distribution (Eyles et al. 1991). Could these discrepancies be consequence of
the standard description of the ICM, in which it is assumed hydrostatic
equilibrium maintained by thermal pressure? We follow the evolution of the ICM,
considering a term of magnetic pressure, aiming at answering the question
whether or not these discrepancies can be explained via non-thermal terms of
pressure. Our results suggest that the magnetic pressure could only affect the
dynamics of the ICM on scales as small as < 1kpc. Our models are constrained by
the observations of large and small scale fields and we are successful at
reproducing available data, for both Faraday rotation limits and inverse
Compton limits for the magnetic fields. In our calculations the radius (from
the cluster center) in which magnetic pressure reaches equipartition is smaller
than radii derived in previous works, as a consequence of the more realistic
treatment of the magnetic field geometry and the consideration of a sink term
in the cooling flow.Comment: 8 pages with 7 figures included. MNRAS accepted. Minor changes in the
section of discussions and conclusions. Also available at
http://www.iac.es/publicaciones/preprints.htm
Response of the warm absorber cloud to a variable nuclear flux in active galactic nuclei
Recent modeling of the warm absorber in active galactic nuclei has proved the
usefulness of constant total (gas plus radiation) pressure models, which are
highly stratified in temperature and density. We explore the consistency of
those models when the typical variation of the flux from the central source is
taken into account. We perform a variability study of the warm absorber
response, based on timescales and our photoionization code TITAN. We show that
the ionization and recombination timescales are much shorter than the dynamical
timescale. Clouds very close to the central black hole will maintain their
equilibrium since the characteristic variability timescales of the nuclear
source are longer than cloud timescales. For more distant clouds, the density
structure has no time to vary, in response to the variations of the temperature
or ionization structure, and such clouds will show the departure from the
constant pressure equilibrium. We explore the impact of this departure on the
observed properties of the transmitted spectrum and soft X-ray variability: (i)
non uniform velocities, of the order of sound speed, appear due to pressure
gradients, up to typical values of 100 km/s. These velocities lead to the
broadening of lines. This broadening is usually observed and very difficult to
explain otherwise. (ii) Energy-dependent fractional variability amplitude in
soft X-ray range has a broader hump around ~ 1-2 keV, and (iv) the plot of the
equivalent hydrogen column density vs. ionization parameter is steeper than for
equilibrium clouds. The results have the character of a preliminary study and
should be supplemented in the future with full time-dependent radiation
transfer and dynamical computations.Comment: 9 pages, 7 figures, accepted for publication by Astronomy &
Astrophysic
The "red shelf" of the Hb line in the Seyfert 1 galaxies RXS J01177+3637 and HS 0328+05
A few Seyfert 1s have a Hb profile with a red wing usually called the "red
shelf". The most popular interpretation of this feature is that it is due to
broad redshifted lines of Hb and [OIII]4959,5007; we have observed two Seyfert
1s displaying a "red shelf" and showed that in these two objects the main
contributor is most probably the HeI 4922,5016 lines having the velocity and
width of the broad Hb component. There is no evidence for the presence of a
broad redshifted component of Hb or [OIII] in any of these two objects.Comment: LaTeX file (uses AA vers. 5.1 class, enclosed), 8 pages, 9 figures.
Accepted for publication in Astronomy & Astrophysics. Also available at
http://www.obs-hp.fr/www/preprints.htm
Miscellaneous observations of active galactic nuclei. II
We observed 37 AGN candidates and classified them on the basis of their
spectroscopic properties; three are confirmed QSOs, one is a BL Lac object,
nine are Seyfert 1 galaxies, four Seyfert 2s, while twenty are HII regions.Comment: LaTeX 2e, 15 pages (4 tables and 9 .eps figures included in text).
Uses L-AA 3.0, epsf.tex and psfig.sty (not included). Accepted to appear in
A&
A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies
We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1
galaxies (NLS1s) or known to have a broad Balmer component narrower than 2000
km/s. Out of these, 19 turned out to have been spectroscopically misidentified
in previous studies; only 64 of the selected objects are genuine NLS1s. We have
spectroscopically observed 59 of them and tried to characterize their Narrow
and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with
Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components
are well fitted by a single Lorentzian profile. This has consequences
concerning their FWHMs and line ratios: when the broad Balmer components are
fitted with a Lorentzian, most narrow line regions have line ratios typical of
Seyfert 2s while, when a Gaussian profile isused for fitting the broad Balmer
components, the line ratios are widely scattered in the usual diagnostic
diagrams (Veilleux & Osterbrock 1987). We find that, in general, the [O III]
lines have a relatively narrow Gaussian profile (~ 200-500 km/s FWHM) with
often, in addition, a second broad (~ 500-1800 km/s FWHM), blueshifted Gaussian
component. We do not confirm that the [O III] lines are weak in NLS1s. As
previously suggested, there is a continuous transition of all properties
between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit
of 2000 km/s used to separate the two species is arbitrary; R_4570, the ratio
of the Fe II to the H_beta fluxes, could be a physically more meaningful
parameter to distinguish them. (abridged abstract)Comment: LaTeX file, 24 pages, 15 figures, uses the new A&A macro (enclosed:
aa5.cls). Figs. 1-5 and 7 are bitmapped; non-bitmapped, high quality figures
are included in the .ps and .pdf versions of the paper, available at
http://www.obs-hp.fr/www/preprints.html. Accepted for publication in
Astronomy & Astrophysic
Determinant Line Bundles and Topological Invariants of Hyperbolic Geometry - Expository Remarks
We give some remarks on twisted determinant line bundles and Chern-Simons
topological invariants associated with real hyperbolic manifolds. Index of a
twisted Dirac operator is derived. We discuss briefly application of obtained
results in topological quantum field theory.Comment: 10 pages. To appear in G@C, special issue devoted to QG, Unified
Models and Strings, to mark 100th Anniversary of Tomsk State Pedagogical
University. Editor - S.D. Odintso
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