1,721,492 research outputs found
HIGH-ENERGY PHENOMENA STUDIED WITH X-RAY POLARIMETRY
No full textAfter more than 30 years since the last X-ray polarimetric measurements, performed in the 70's by the OSO-8 satellite, thanks to recent technological advances, polarimetry is considered again as a viable technique for studing X-ray sources. In this contribution the author briefly discusses a couple of astrophysical situations, related to the topics of this conference, where X-ray polarimetry can be extremely useful. The author also discusses the observational perspectives, listing the main future space missions (proposed or even already approved) carrying on-board an X-ray polarimeter
X-RAY-POLARIZATION PROPERTIES OF A CENTRALLY ILLUMINATED ACCRETION DISK
No full textThe polarization of the X-rays reflected by a centrally illuminated, optically thick and geometrically thin accretion disc is calculated as a function of the source and disc parameters. The degree of polarization of the reflected radiation depends strongly on the disc inclination, and could be greater than 20 per cent; the polarization angle is 90-degrees, i.e. the polarization vector lies in the meridian plane. Due to the dilution of the primary source, assumed unpolarized, the net polarization depends strongly on photon energy, and could reach values as high as approximately 6 per cent at energies greater than a few tens of keV. When relativistic effects in the Schwarzschild metric are taken into account, the degree of polarization generally increases, and the polarization angle becomes greater than 90-degrees. The model could be tested by the SXRP experiment for several galactic X-ray binaries, and at least for one active galaxy, i.e. Centaurus A
The iron K alpha Compton shoulder in transmitted and reflected spectra
No full textWe calculate the equivalent width of the core, and the centroid energy and relative flux of the first-order Compton shoulder of the iron Kalpha emission line from neutral matter. The calculations are performed with Monte Carlo simulations. We explore a large range of column densities for both transmitted and reflected spectra, and study the dependence on the iron abundance. The Compton shoulder is now becoming observable in many objects thanks to the improved sensitivity and/or energy resolution of the XMM-Newton and Chandra satellites, and the present work aims to provide a tool to derive information on the geometry and element abundances of the line-emitting matter from Compton shoulder measurements
Broad band spectral properties of AGNs and quasars, observations and theory
No full textWe review and discuss the main BeppoSAX results on Radio-Quiet Active Galactic Nuclei, both Seyfert Is and Seyfert 2s. We will also present new results from simultaneous BeppoSAX/XMM-Newton observations of Seyfert is and Compton-thin Seyfert 2, and from XMM-Newton alone (confirming and refining previous BeppoSAX results) on Compton-thick Seyfert 2s
IRON K-ALPHA RESONANT ABSORPTION IN WARM ABSORBERS AROUND ACTIVE GALACTIC NUCLEI
No full textRecent ROSAT observations have established the presence of ionized matter along the line of sight in active galactic nuclei (the warm absorber). Here we investigate the iron Kalpha resonant absorption from the ionized matter, and find that the total equivalent width could be very relevant, up to several tens of eV. We point out its importance in determining the physical status and the geometry of the warm absorber. On the other hand, we warn that it can confuse, if neglected, the measurement of the broad iron line emitted by the accretion disc
Obscured active galactic nuclei: the hidden side of the X-ray Universe
No full textContents: Introduction. The properties of circumnuclear matter: physical properties of reflecting matter - Compton-thin or Compton-thick' - Two different regions' Obscured AGN and the unification model. Obscured AGN and the X-ray and IR cosmic backgrounds
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