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