Reflection at large distance from the central engine in Seyferts

We consider the possibility that most of the reflection component, observed in the hard X-ray spectra of Seyfert galaxies, could be formed on an extended medium, at large distance from the central source of primary radiation (e.g. on a torus). Then, the reflector cannot respond to the rapid fluctuations of the primary source. The observed reflected flux is controlled by the time-averaged primary spectrum rather than the instantaneous (observed) one. We show that this effect strongly influence the spectral fits parameters derived under the assumption of a reflection component consistent with the primary radiation. We find that a pivoting primary power-law spectrum with a nearly constant Comptonised luminosity may account for the reported correlation between the reflection amplitude $R$ and the spectral index $\Gamma$.Comment: Proceeding of the meeting "X-ray emission from accretion onto black hole" 20-23 June 2001, Hopkins University, Baltimore, USA (style file jhuwkshp.sty included

X-ray polarimetric signatures induced by spectral variability in the framework of the receding torus model

Obscuring circumnuclear dust is a well-established constituent of active galactic nuclei (AGN). Traditionally referred to as the receding dusty torus, its inner radius and angular extension should depend on the photo-ionizing luminosity of the central source. Using a Monte Carlo approach, we simulate the radiative transfer between the multiple components of an AGN adopting model constraints from the bright Seyfert galaxy NGC 4151. We compare our model results to the observed near-IR to UV polarization of the source and predict its X-ray polarization. We find that the 2-8 keV polarization fraction of a standard AGN model varies from less then a few percent along polar viewing angles up to tens of percent at equatorial inclinations. At viewing angles around the type-1/type-2 transition the X-ray polarization variability differs between a static or a receding torus scenario. In the former case, the expected 2-8 keV polarization of NGC 4151 is found to be 1.21% +/- 0.34% with a constant polarization position angle, while in the later scenario it varies from 0.1% to 6% depending on the photon index of the primary radiation. Additionally, an orthogonal rotation of the polarization position angle with photon energy appears for very soft primary spectra. Future X-ray polarimetry missions will be able to test if the receding model is valid for Seyfert galaxies seen at a viewing angle close to the torus horizon. The overall stability of the polarization position angle for photon indexes softer than {\Gamma} = 1.5 ensures that reliable measurements of X-ray polarization are possible. We derive a long-term observational strategy for NGC 4151 assuming observations with a small to medium-size X-ray polarimetry satellite.Comment: 10 pages, 8 Figures, accepted for publication in A&

A multi-flow model for microquasars

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/gamma-rays, by varying the transition radius r_J and disc accretion rate independently. Large values of r_J and low accretion rate correspond to Quiescent and Hard states. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expect to form at the jet basis. When r_J becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large accretion rate, an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions.Comment: 12 pages, 3 figures. Proceedings of ``High Energies in the Highlands'', Fort-William, 27 June-1 July 200

BeppoSAX observations of the quasar Markarian 205

We present the first BeppoSAX observation (0.1 to 220 keV) of the quasar Mrk 205. We have searched for the unusual Fe line profile claimed in the XMM-Newton spectrum which has been widely discussed in recent literature. We find no evidence for a broad, ionized Fe line component in our data. We detect for the first time a Compton hump in this object. Besides, when this component is included in the fit, the line strength diminishes, in agreement with a recent re-analysis of the XMM-Newton data, but with better constraints on the reflection component thanks to the PDS instrument (15-220 keV). We interpret this fact as another indication for illumination of a distant and cold material rather than reprocessing in the highly ionized inner parts of an accretion disk. We cannot constrain the presence of a high energy cutoff but we confirm the existence of a variable soft excess (one year timescale).Comment: 13 pages, 12 figures, accepted for publication in A&