Relationship between X-ray and ultraviolet emission in 3C 273

In 3C 273, ultraviolet flux and X-ray flux measured by BATSE are not well correlated, contrarily to predictions of several models, unless the X-ray flux lags the UV emission by 1.75 yr. The absence of observed correlation at small lag cannot be due to spectral variability. A Comptonizing corona model is however compatible with all UV and X-ray observations covering the BATSE period.Comment: LaTeX, 4 pages, 6 figures. espcrc2.sty style file included. Poster contribution to the symposium "The Active X-ray Sky: Results from BepppoSAX and Rossi-XTE", Rome, October 199

ISOPHOT Observations of Narrow-Line Seyfert 1 Galaxies

Broad infrared spectra (7-200 micrometer) of four NLS1 galaxies, obtained with the imaging photo-polarimeter (ISOPHOT) on board the Infrared Space Observatory (ISO), are presented. The infrared luminosities and temperatures, opacities and sizes of the emitting dust components are derived. A comparison between the observed infrared spectra and the optical emission line fluxes of a sample of 16 NLS1 galaxies suggests that these objects suffer different degrees of dust absorption according to the inclination of the line of sight with respect to the dust distribution.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

The application of slim disk models to ULX: the case of M33 X-8

A comparative XMM-Newton archival data spectral study of the ultraluminous X-ray source (ULX) M33 X-8 has been performed by using both the standard disk model and the newly developed slim disk models. The results of this analysis tend to confirm the hypothesis that M33 X-8 is an X-ray binary with a stellar-mass black hole accreting at super-Eddington rate.Comment: 6 pages, 4 figures, accepted for publication on Advances in Space Research, Special Issue Proceedings of 35th COSPAR (Paris, France, 18-25 July 2004

Active Galactic Nuclei at the Crossroads of Astrophysics

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especially in the areas of high-resolution and high-fidelity imaging and spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These studies will address in detail a number of critical issues in AGN research such as processes in the immediate vicinity of supermassive black holes, physical conditions of broad-line and narrow-line regions, formation and evolution of accretion disks and relativistic outflows, and the connection between nuclear activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical Symposia Serie

Radio and Gamma-Ray Astronomy

Progress in the understanding of many astrophysical objects requires the use radio and high energy data. This is particularly true in high energy astrophysics when considering compact objects. The emission processes emitting radio and high energy photons are furthermore deeply related. However, the limitations in the observations, render often the comparison of radio and gamma-ray data difficult

Multi-zone warm and cold clumpy absorbers in three Seyfert galaxies

International audienceAims: We present the first detailed X-ray analysis of three active galactic nuclei, the Seyfert 1 galaxies UGC 3142 and ESO 140-43, and the Seyfert 2 galaxy ESO 383-18, to study the geometry and the physical characteristics of their absorbers. Methods: High-quality XMM-Newton EPIC and RGS data were analyzed as well as Swift/XRT and BAT and INTEGRAL IBIS/ISGRI data to cover the 0.3-110 keV energy range. For ESO 140-43 also XMM-Newton/OM and Swift/UVOT data were used. We studied the variability of the three AGN on a time-scale of seconds using the EPIC/PN light curves, and the long-term time-scale variability of ESO 140-43 using two observations performed six months apart by XMM-Newton. Results: The spectra of the three Seyfert galaxies present a "soft excess" at energies E < 2 keV above a power law continuum that can be modeled by complex absorption, without any additional emission component. The X-ray sources in UGC 3142 and ESO 383-18 are absorbed by two layers of neutral material, with covering fractions f1 ≃ 0.92 and f2 ≃ 0.57 for UGC 3142, and f1 ≃ 0.97 and f2 ≃ 0.86 for ESO 383-18. While the clumpy absorber could be part of a disk wind or of the broad line region for UGC 3142, for ESO 383-18 a clumpy torus plus Compton thin dust lanes are more likely. The spectra of ESO 140-43 can be well fitted with a power law absorbed by three clumpy ionized absorbers with different covering factors, column densities, and ionization parameters, likely part of a moving clumpy system, which could be a disk wind or the broad line region. The strong spectral and flux variability on a time-scale of six months seen in ESO 140-43 is likely due to changes in the moving absorbers. We were able to detect the variation of the covering factor of one of the three ionized absorbers on a kilo-seconds time-scale in the EPIC light-curve of ESO 140-43

The Far-Infrared emission of Radio Loud and Radio Quiet Quasars

Continuum observations at radio, millimetre, infrared and soft X-ray energies are presented for a sample of 22 quasars, consisting of flat and steep spectrum radio loud, radio intermediate and radio quiet objects. The primary observational distinctions, among the different kinds of quasars in the radio and IR energy domains are studied using large observational datasets provided by ISOPHOT on board the Infrared Space Observatory, by the IRAM interferometer, by the sub-millimetre array SCUBA on JCMT, and by the European Southern Observatory (ESO) facilities IRAC1 on the 2.2 m telescope and SEST. The spectral energy distributions of all quasars from radio to IR energies are analyzed and modeled with non-thermal and thermal spectral components. The dominant mechanism emitting in the far/mid-IR is thermal dust emission in all quasars, with the exception of flat spectrum radio loud quasars for which the presence of thermal IR emission remains rather uncertain, since it is difficult to separate it from the bright non-thermal component. The dust is predominantly heated by the optical/ultraviolet radiation emitted from the external components of the AGN. A starburst contributes to the IR emission at different levels, but always less than the AGN (< 27%). The distribution of temperatures, sizes, masses, and luminosities of the emitting dust are independent of the quasar type.Astronom

IBAS, the

We report on the INTEGRAL Science Data Centre (ISDC) BURST ALERT SYSTEM, designed to automatically distribute GRB positions as measured with INTEGRAL within tens of seconds after the burst